Apparatus and methods for obscured feature detection

ABSTRACT

An obscured feature detector can include a plurality of sensor plates and a common plate. The sensor plates may be arranged linearly to form a sensor array. The common plate may extend along the sensor array and have a length that is shortened. An end sensor plate at an end of the sensor array has a smaller area than a non-end sensor plate that is not at the end of the sensor array. A controller coupled to the sensing circuit can analyze the capacitances measured by the sensing circuit. One or more indicators are coupled to the controller, and each can be selectively set to identify a location of an obscured feature behind a surface, or otherwise indicate variances of capacitance measurements along the sensor array. Other disclosed obscured feature detectors include a plurality of sensor plates arranged radially around a center point.

TECHNICAL FIELD

The present disclosure relates generally to devices to detect a presenceof obscured features behind opaque, solid surfaces, and morespecifically to devices to locate beams and studs behind walls andjoists beneath floors.

BACKGROUND

Locating obscured features such as beams, studs, joists and otherelements behind walls and beneath floors is a common problem encounteredduring construction, repair and home improvement activities. Forexample, often a desire arises to cut or drill into a wall, floor, orother supported surface with the aim of creating an opening in thesurface while avoiding the underlying support elements. In theseinstances, knowing where the support elements are positioned beforebeginning can be desirable so as to avoid cutting or drilling into thesupport elements. On other occasions, one may desire to anchor a heavyobject such as a picture or shelf to a support element obscured by asupported surface. In these cases, it is often desirable to install afastener through the supported surface in alignment with an underlyingsupport element. However, with the wall, floor or supported surface inplace, the location of the support element is not visually detectable.

A variety of rudimentary techniques have been employed in the past withlimited success to address the problem of locating underlying featuresobscured by an overlying surface. These techniques include driving smallpilot nails through various locations in the overlying surface until anunderlying support element is encountered and then covering over holesin the surface that did not reveal the location of the underlyingsupport element. A less destructive technique comprises tapping on theoverlying surface with the aim of detecting audible changes in the soundwhich emanates from the surface when there is a support element beneathor behind the area of the surface being tapped. This technique isineffective, however, because the accuracy of the results dependsgreatly on the judgment and skill of the person tapping and listening tosearch for the underlying support element, and because the sound emittedby the tapping is heavily influenced by the type and density of thesurface being examined.

Magnetic detectors have also been employed to find obscured supportelements with the detector relying on the presence of metallicfasteners, such as nails or screws, in the wall and support element totrigger a response in the detector. However, since metallic fastenersare spaced at discrete locations along the length of a support, amagnetic detector may pass over a length of the support where nofasteners are located, thereby failing to detect the presence of theobscured support element.

Electronic sensors have also been employed to detect obscured featuresbehind opaque surfaces. These detectors sense changes in capacitance onthe examined surface that result from the presence of featurespositioned behind, beneath or within the surface. These changes incapacitance are detectable through a variety of surfaces such as wood,sheetrock, plaster and gypsum and do not rely on the presence of metalfasteners in the surface or obscured feature for activation of thesensor. However, conventional electronic detectors may suffer from asignificant shortcoming. Conventional obscured feature detectors mayhave difficulty accurately compensating for the thickness and density ofthe detected surface, which negatively impact accuracy.

SUMMARY

The present disclosure advantageously addresses one or more of theaforementioned deficiencies in the field of obscured feature detectionby providing an accurate, simple to use and inexpensively manufacturedobscured feature detector. The detector can be employed by placing thedevice against the examined surface and reading the location of allfeatures present beneath the surface where the device is positioned. Thedetector is able to accurately read through different surface materialsand different surface thicknesses.

Additional aspects and advantages will be apparent from the followingdetailed description of preferred embodiments, which proceeds withreference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an advanced obscured feature detector, according toone embodiment, placed on a piece of sheetrock and detecting an obscuredfeature.

FIG. 2 is a perspective view of the obscured feature detector of FIG. 1.

FIG. 3 is an illustrative drawing that shows sensor plates and activatedindicators of the obscured feature detector of FIG. 1, with theactivated indicators signaling a position of the hidden obscuredfeature.

FIG. 4 is a diagram of a circuit of an obscured feature detector,according to one embodiment.

FIG. 5 is a diagram of a controller of an obscured feature detector,according to one embodiment.

FIG. 6 is a cross-sectional view of an obscured feature detector,according to one embodiment, including a housing, with light pipes and abutton, and a printed circuit board.

FIG. 7 is a prior art obscured feature detector placed on acomparatively thinner surface.

FIG. 8 is a prior art obscured feature detector placed on acomparatively thicker surface.

FIG. 9 shows a side view of a prior art obscured feature detector,illustrating primary sensing field zones for several sensor plates.

FIG. 10 shows an elevation view of a bottom surface of a prior artobscured feature detector, illustrating the primary sensing field zonesfor several sensor plates.

FIG. 11 is a flow diagram of a method of detecting an obscured featurebehind a surface, according to one embodiment.

FIG. 12 is a prior art plate configuration for an obscured featuredetector with a common plate.

FIG. 13 is a plate configuration for an obscured feature detector with ashortened common plate.

FIG. 14 illustrates the electric field lines for the prior art plateconfiguration of FIG. 12.

FIG. 15 illustrates the electric field lines for the plate configurationof FIG. 13.

FIG. 16 illustrates the electric field lines for a sensor plate arraywith multiple common plates.

FIG. 17 is a flow chart illustrating a method of detecting an obscuredfeature behind a surface with a plate configuration with a shortenedground plane, according to one embodiment.

FIG. 18 illustrates the electric field lines for a sensor plate arraywith narrow end-plates.

FIG. 19 illustrates the electric field lines for a sensor plate arraywith trapezoidal end-plates.

FIG. 20 illustrates an obscured feature detector, according to oneembodiment, positioned on a piece of sheetrock and detecting an obscuredfeature.

FIG. 21 is a perspective view of the obscured feature detector of FIG.20.

FIG. 22 is an illustrative drawing that shows sensor plates andactivated indicators of the obscured feature detector of FIG. 20, withthe activated indicators signaling a position of the hidden obscuredfeature.

FIG. 23 is a diagram of a circuit of an obscured feature detector,according to one embodiment.

FIG. 24 is a diagram of a controller of an obscured feature detector,according to one embodiment.

FIG. 25 illustrates a routing of sensor plate traces of an obscuredfeature detector, according to one embodiment. In the illustratedembodiment, each of the sensor plate traces has substantially similartrace length and the traces are surrounded by an active shield.

FIG. 26 is a diagram of a sensor plate configuration of an obscuredfeature detector, according to another embodiment.

FIG. 27 is a cross-sectional view of an obscured feature detector,according to one embodiment, including a housing, with light pipes and abutton, and a printed circuit board.

FIG. 28 illustrates a sensor plate group with four sensor plates.

FIG. 29 illustrates a sensor plate group with six sensor plates.

FIG. 30 is a prior art obscured feature detector placed on acomparatively thinner surface.

FIG. 31 is a prior art obscured feature detector placed on acomparatively thicker surface.

FIG. 32 shows a side view of a prior art obscured feature detector,illustrating primary sensing field zones for several sensor plates.

FIG. 33 shows an elevation view of a bottom surface of a prior artobscured feature detector, illustrating the primary sensing field zonesfor several sensor plates.

FIG. 34 illustrates a diagrammatic side view of a chassis of a coreapparatus of a surface-conforming obscured feature detector, accordingto one embodiment.

FIG. 35 is a perspective view of the chassis of the core apparatus ofFIG. 34.

FIG. 36 is a flow diagram of a method of detecting an obscured featurebehind a surface, according to one embodiment.

FIG. 37 illustrates two different printed circuit boards in a stackedconfiguration.

FIG. 38 illustrates a prior art configuration for routing and shieldingthe sensor plate traces from the controller to the sensor plates.

FIG. 39 is a cross-sectional view of an obscured feature detector,according to one embodiment, illustrating electric field patterns.

FIG. 40 is a cross-sectional view of an obscured feature detector,according to another embodiment, illustrating electric field patterns.

FIG. 41 is a sensor plate cluster that includes an active shield center,eight sensor plates, an active shield plate, and a common plate.

FIG. 42 is a sensor plate cluster that includes an active shield center,eight sensor plates, and an active shield plate.

FIG. 43 is a side view of an obscured feature detector, according to oneembodiment, that is placed on a surface and that includes a sensor platecluster similar to that shown in FIG. 42.

FIG. 44 is a sensor plate cluster that includes eleven sensor plates, anactive shield plate, and a common plate, and the end sensor plates haveless surface area than the sensor plates that are not at the ends.

FIG. 45 is a side view of an obscured feature detector, according to oneembodiment, that is placed on a surface and that includes a sensor platecluster similar to that shown in FIG. 44.

FIG. 46 is a side view of an obscured feature detector, according toanother embodiment, that is placed on a surface.

In the following description, reference is made to the accompanyingdrawings that form a part thereof, and in which is shown by way ofillustration specific exemplary embodiments in which the invention maybe practiced. These embodiments are described in sufficient detail toenable those skilled in the art to practice the technology andembodiments described herein, and it is to be understood thatmodifications to the various disclosed embodiments may be made, andother embodiments may be utilized, without departing from the spirit andscope of the present disclosure. The following detailed description is,therefore, not to be taken in a limiting sense.

DETAILED DESCRIPTION

Many presently available stud finders (e.g., obscured feature detectors)use capacitance to detect obscured features behind a surface.Capacitance is an electrical measure of an object's ability to hold orstore charge. A common form of an energy storage device is the parallelplate capacitor whose capacitance is approximated by: C=εr εo A/d, whereA is the overlapping area of the parallel plates, d is the distancebetween the plates, εr is the relative static permittivity (ordielectric constant of the material between the plates), and εo is aconstant. A dielectric material is an electrical insulator that can bepolarized by applying an electric field. When a dielectric is placed inan electric field, the molecules shift from their average equilibriumpositions causing dielectric polarizations. Because of dielectricpolarizations, positive charges are shifted toward the negative edge ofthe field, and negative charges shift in the opposite direction.

The dielectric constant (εr) of air is one, while most solidnon-conductive materials have a dielectric constant greater than one.Generally, it is the variations in the dielectric constants ofnon-conductive solids that enable conventional capacitive sensors towork.

When the sensor plates on an obscured feature detector are placed on awall at a location with no support behind the wall, the detectormeasures the capacitance of the wall and the air behind it. When placedin a position having a support behind the wall, the detector thenmeasures the capacitance of the wall and the support, which has a higherdielectric constant than air. As a consequence, the detector registersan increase in capacitance which can then be used to trigger anindicating system.

In presently available obscured feature detectors a set of identicalsensor plates are typically arranged in a linear fashion (see, e.g.,FIG. 10). Each of the sensor plates performs a sensor reading of thesurface. The sensor readings are then compared. The sensor plates thathave the highest sensor readings are interpreted to be the locations ofobscured features. However, sensor plates that are near the ends of thegroup may not respond to obscured features in the same manner as theplates that are near the center. This issue may be particularly evidentwhen the obscured feature detector is moved from a thinner, or lessdense, surface to a thicker, or more dense, surface.

Ideally, each of the sensor plates on a thicker surface would havesimilar sensor readings to each other, because the sensor plates are allon the same surface, with no obscured features present. However, thesensor readings of the sensor plates near the ends may see a largerreading increase than the sensor plates near the center. The sensorplates that are at the ends are alone in creating the electric fieldsthat are beyond the group of sensor plates. As a result, the sensorplates near the end may respond with a disproportionately higher readingwhen placed on a thicker surface. Accordingly, the controller may havedifficulty determining if the elevated sensor readings are due to thepresence of an obscured feature, or due to the detector being placed ona thicker surface. This disclosure provides a solution.

In obscured feature detectors with multiple sensor plates it isdesirable for each sensor plate to have a similar response to the sameobscured feature. To ensure a similar response from each sensor plate,proper geometric shape and arrangement of the sensor plates can ensurean equivalent response to an obscured feature. Improved shielding ofsensor plate traces may also improve performance. In addition, enhancedelectrical coupling of the user to the sensing circuit may provideimproved performance. Also, a mechanism to ensure that the sensor platesare flat against the surface may improve performance.

The present disclosure is directed to obscured feature detectors andmethods of detecting obscured feature detectors. In the exemplaryembodiments, an obscured feature detector comprises a group of sensorplates, a multi-layer printed circuit board (PCB), a sensing circuit, acontroller, a display circuit, a power controller, and/or a housing.

The disclosed embodiments help maintain uniform or near uniform electricfield lines generated by the group of sensor plates. Specifically, theelectric field of two end sensor plates in the group of sensor plates issubstantially similar to the electric field of the non-end sensorplates. The electric fields produced by the end sensor plates and thenon-end sensor plates may be oriented transverse relative to each other.

The disclosed embodiments enable more accurate identification of alocation of an obscured feature. The disclosed embodiments can alsoinstantly and accurately read through a variety of surfaces withdifferent dielectric constants. In addition, the presently disclosedembodiments improve the ability to instantly and accurately read througha variety of surface thicknesses.

The disclosed embodiments also create a detector that is easier to use.Many prior art detectors require more steps, and more time and moreproficiency, in order to recalibrate the unit to different surfaces todetermine the locations of obscured features. The disclosed embodimentsprovide more reliable sensor readings. The sensor readings from thesensor plates self-adjust to the detected surface and provide a morereliable reading and have the ability to detect features more deeply.The sensor readings have significantly less surface-thickness-inducedreading error. With this reading error removed, the disclosedembodiments can detect objects more deeply.

The present disclosure will now be described more fully with referenceto the accompanying drawings. This disclosure may, however, be embodiedin many different forms and should not be construed as limited to theembodiments set forth herein; rather, these embodiments are provided byway of illustration only so that this disclosure will be thorough, andfully convey the full scope to those skilled in the art.

FIG. 1 illustrates an obscured feature detector 1, according to oneembodiment, placed on a piece of sheetrock 2 (or similar surface) anddetecting an obscured feature 3. FIG. 2 is a perspective view of theobscured feature detector 1 of FIG. 1. FIG. 3 shows a sensor side of theobscured feature detector 1, which includes a plurality of sensor plates5 and a shortened common plate 33.

With reference to FIGS. 1-3, generally and collectively, the obscuredfeature detector 1 includes three or more sensor plates 5, a sensingcircuit (see FIG. 4), one or more indicators 6, one or more proximityindicators 39, and a housing 19 to provide or otherwise accommodate ahandle 14, an active shield plate 23, and a battery cover 28.

The three or more sensor plates 5 each can take a sensor reading thatvaries based on a proximity of the sensor plate 5 to one or moresurrounding objects and on a material property of each of the one ormore surrounding objects. The three or more sensor plates 5 maycollectively create a sensing field. Each individual sensor plate 5 ofthe three or more sensor plates 5 may create a corresponding primarysensing field zone that may be a geometric three-dimensional volumewithin the sensing field where the individual sensor plate 5 contributesmore strongly to the sensing field than any other of the three or moresensor plates 5. The three or more sensor plates 5 may all createprimary sensing field zones that are geometrically similar. The sensingcircuit may couple to the three or more sensor plates 5 to measure thesensor readings of the three or more sensor plates 5.

Each sensor plate 5 forms a first end of a corresponding electric field.The electric field is produced or received at the sensor plates 5. Anarea on the common plate 33 may form a second end of the correspondingelectric field of each sensor plate 5. The common plate 33 has a lengthextending along one side of each of the sensor plates 5. The length ofthe common plate 33 is less than a collective linear dimension of thesensor plates 5. In some embodiments, the common plate 33 is coupled toa non-changing voltage. In some embodiments the common plate 33 iscoupled to the circuit ground. In some embodiments the common plate 33is coupled to an alternating signal.

In some embodiments each sensor plate 5 may be part of a group 7 orarray of sensor plates 5. Each group 7 may include two or more sensorplates 5 and may also include an active shield plate 23. The sensorplates 5 and active shield plate 23 may be on different planes.Nevertheless, if they are driven simultaneously, in some embodiments,they may be part of the same group 7 of sensor plates 5. Each sensorplate 5 has a geometry that is defined by its shape. Each sensor plate 5also has a perimeter. In some embodiments the perimeter may be composedof multiple segments. In some embodiments each segment of the perimeteris either an internal border 10 or an external border 11. In someembodiments, if a sensor plate 5 has a segment of the perimeter that isadjacent to the perimeter of the group 7, then said segment comprises anexternal border 11. In some embodiments, if a sensor plate 5 has asegment of the perimeter that is not adjacent to the perimeter of thegroup 7, then said segment comprises an internal border 10.

In some embodiments to sense the location of an obscured feature 3, asensor plate 5 may be driven with a current source, and the obscuredfeature detector 1 measures the time it takes for the sensor plate 5 toreach a certain threshold voltage, thereby achieving a sensor reading.In other embodiments a charge-share mechanism, or sigma delta converteris used to achieve a sensor reading. Other sensing circuits may also beemployed. In other embodiments a radio frequency signal is placed on thesensor plates 5 to achieve a sensor reading. In each of theseembodiments a signal is driven on the sensor plate(s) 5 to be sensed.

In some embodiments, only a single sensor plate 5 may be driven at atime. In these embodiments the single sensor plate 5 may be alone increating the sensing field.

In some embodiments, the group 7 of sensor plates 5 may all be drivenwith the same signal simultaneously. In these embodiments the group 7 ofsensor plates 5 may create the sensing field. In some embodimentsmultiple sensor plates 5 may be driven simultaneously each with the samesignal, although possibly only a single sensor plate 5 may be sensed.Advantageously driving multiple sensor plates 5 simultaneously maycreate field lines that go deeper into an obscured surface than may bepossible if only a single sensor plate 5 is driven. Deeper field linesmay make it possible to sense more deeply. In some embodiments the group7 of sensor plates 5 and the active shield plate 23 may all be drivenwith the same signal simultaneously, which together would create thesensing field.

Each sensor plate 5 has a primary sensing field zone. In someembodiments the primary sensing field zone is a geometricthree-dimensional volume of the sensing field and associated field lineswhere the individual sensor plate 5 is able to sense more strongly thanthe active shield plate 23 (if present) or any other sensor plate 5. Insome embodiments it is desirable for each sensor plate 5 to have similarprimary sensing field zones. In some embodiments it is desirable foreach sensor plate 5 to have primary sensing field zones that aregeometrically similar and to have similar sensing fields within theirrespective primary sensing field zones.

FIG. 3 illustrates thirteen sensor plates 5 arranged linearly to form asensor array 7. Each of the sensor plates 5 is rectangular. Each sensorplate 5 is configured to take a sensor reading that varies based on theproximity of the sensor plate 5 to one or more surrounding objects andon a material property of each of the one or more surrounding objects.

In some embodiments, as shown in FIG. 3, the sensor array 7 may comprisesensor plates 5 that each have a similar geometry. In some embodimentsthe distance between adjacent sensor plates 5 may be approximately 2.0mm. As shown, a shortened common plate 33 extends along the sensor array7 along one side of each of the sensor plates 5. The length of theshortened common plate 33 is less than the collective linear dimensionof the sensor array 7. In some embodiments, the shortened common plate33 may not extend along a side of one or both of the end sensor plates.

In FIG. 3 a sensing field may be created collectively by the sensorplates 5. In some embodiments an active shield plate 23 may contributeto the sensing field. In the embodiment of FIG. 3 each of the sensorplates 5 may have similar primary sensing field zones. In thisembodiment, the shortened common plate 33 causes each sensor plate 5 tohave primary sensing zones that are more geometrically similar asexplained in more detail with reference to FIGS. 12, 15, and 16.Likewise, each of the sensor plates 5 may also have similar sensingfields within their respective primary sensing field zones. As a result,an obscured feature detector 1 that is built with a configuration ofFIG. 3 may offer improved performance. When the obscured featuredetector 1 is moved from a thin surface to a thicker surface the sensorreadings for each of the sensor plates 5 may have a similar increase invalue.

In some embodiments a sawtooth-shape border or perimeter may have thesame effective border as a straight-line border that does not have asawtooth. In some embodiments a border with a very slight curve may havethe same effective border as a straight-line border that does not have aslight curve. In some embodiments a sensor plate 5 with a slot in it hasthe same effective geometry as an otherwise equivalent sensor plate 5without a slot. In some embodiments a sensor plate 5 with a small holein it may have the same effective geometry as an equivalent sensor plate5 without a hole. Many other geometries are possible that may beeffectively equivalent to other substantially equivalent geometries.Many other borders are possible that may effectively be equivalent toother substantially equivalent borders. If a geometry or a border has aproperty that is effectively equivalent to another geometry or border,then the two may be considered to be similar.

In some embodiments the group 7 of sensor plates 5 is configured suchthat each sensor plate 5 in the group 7 has the same geometry. In someembodiments each of the sensor plates 5 in the group 7 is radiallysymmetrical.

The plurality of indicators 6 may be toggled between a deactivated stateand an activated state to indicate a location of a region of relativehigh sensor reading. Activated indicators 4 can indicate the position ofthe obscured feature 3. Proximity indicators 39 can indicate that theobscured feature detector 1 may be near the obscured feature 3.

In FIGS. 1-3, the indicators 6 are positioned on a layer above thesensor plates 5. In some embodiments there may be an active shield plate23 between the sensor plates 5 and the indicators 6 so that theindicators 6 do not interfere with the function of the sensor plates 5.In some embodiments it may be desirable to position the indicators 6 ona layer above the sensor plates 5.

In some embodiments, a layer of protective material is mounted to thebottom of the obscured feature detector housing, such that there is alayer of protective material between the surface 2 (e.g., sheetrock) andthe obscured feature detector 1. In some embodiments, the protectivematerial has the interior substantially filled such that it issubstantially free from cavities. In some embodiments the protectivematerial is unlike felt, Velcro, cloth, or other materials that have aninterior with cavities. The layer of protective material may serve thepurpose of protecting the bottom of the obscured feature detector 1 fromdamage due to knocks, bumps, and wear-and-tear. The protective materialcould be made from a solid piece of material, such as plastic or othersolid non-conductive materials. A solid layer of plastic may provide alow friction surface that would allow the obscured feature detector 1 toslide across the wall. Although some embodiments of the obscured featuredetector 1 do not require sliding to operate, a low friction surface maybe useful to some users who may choose to move the obscured featuredetector 1 from position to position by sliding it.

The protective layer of plastic may be mounted with a pressure sensitiveadhesive, glue, or other means. The layer of protective material may bea complete layer that covers the entire surface; it may be rectangularstrips, round pieces, or other layers of plastic with other geometries.

A protective material that is substantially filled such that it issubstantially free from cavities may build up less static charge thanprior art solutions and may advantageously provide for more consistentsensor readings.

In some embodiments the protective material is UHMW-PE (Ultra-HighMolecular Weight Polyethylene). UHMW-PE has a low coefficient offriction. UHMW-PE also absorbs very little moisture which may provideincreased immunity from changes in humidity, and may provide enhancedimmunity from changes in humidity.

FIG. 4 is a diagram of a circuit of an obscured feature detector 1,according to one embodiment. The circuit includes a multiplexer 18, apower controller 20, a display circuit 25, a sensing circuit 27, and acontroller 60.

The power controller 20 may include a power source 22 and an on-offbutton 24. The power source 22 can comprise an energy source forpowering the indicators 6 and supplying power to acapacitance-to-digital converter 21, and the controller 60. In someembodiments, the power source 22 can comprise a DC battery supply. Theon-off switch 24 can be used to activate the controller 60 and othercomponents of the obscured feature detector 1. In some embodiments, theon-off switch 24 comprises a push-button mechanism that activatescomponents of the obscured feature detector 1 for a selected timeperiod. In some embodiments the push button activates the componentssuch that the components remain activated until the button is released.In some embodiments the on-off switch 24 comprises a capacitive sensorthat can sense the presence of a finger or thumb over the button. Insome embodiments, the on-off switch 24 can comprise a toggle switch orother types of buttons or switches.

The display circuit 25 may include one or more indicators 6 that areelectronically coupled to the controller 60.

The sensing circuit 27 may include a voltage regulator 26 and thecapacitance-to-digital converter 21. In some embodiments, as shown inFIG. 4, the sensing circuit 27 comprises a plurality of sensors, thevoltage regulator 26, and the capacitance-to-digital converter 21. Thevoltage regulator 26 may be used to condition the output of the powercontroller 20, as desired. In some embodiments the voltage regulator 26is placed as near as possible to the capacitance-to-digital converter21, which may provide a better power source 22 to thecapacitance-to-digital converter 21. The sensing circuit 27 can beelectrically coupled to the controller 60. One or more sensor platetraces 35, or electrically conductive paths on the PCB, may connect theindividual sensor plates 5 to the capacitance-to-digital converter 21.The connection of the sensor plates 5 to the capacitance-to-digitalconverter 21 may be made via the multiplexer 18. The multiplexer 18 canindividually connect the sensor plates 5 to the capacitance-to-digitalconverter 21.

In some embodiments the multiplexer 18 may connect a single sensor plate5 to the sensing circuit 27. In some embodiments, the multiplexer 18 mayconnect more than one adjacent sensor plate 5 to the sensing circuit 27.In some embodiments, the multiplexer 18 may connect more than onenon-adjacent sensor plate 5 to the sensing circuit 27. In someembodiments, the multiplexer 18 is configured so that the sensingcircuit 27 measures the capacitance of one sensor plate 5. In someembodiments, the multiplexer 18 is configured so that the sensingcircuit 27 measures the aggregate capacitance of two or more sensorplates 5.

Each individual sensor plate 5 of a group 7 can be independentlyconnected to the capacitance-to-digital converter 21 via the multiplexer18. In some embodiments, the group 7 itself is composed of layers ofcopper on a PCB.

In some embodiments a two-layer PCB is configured as a sensor plateboard 40 (see FIG. 6). In some embodiments a first layer of the sensorplate board 40 comprises the sensor plates 5, and a second layer of thesensor plate board 40 comprises a shield. In some embodiments, theshield is composed of a layer of copper that covers the entire surfaceof the second layer of the PCB. In some embodiments the layer of copperis covered with a non-conductive layer of soldermask. In someembodiments there are holes in the layer of soldermask. In someembodiments, the holes in the layer of soldermask comprise solder padsthat are suitable for making solder bonds.

In some embodiments a four-layer PCB is configured as an interconnectionboard that has interconnections suitable for connecting circuitrycomponents. In some embodiments the interconnection board is configuredwith four layers of interconnections that are suitable forinterconnecting the sensing circuit 27, the controller 60, and thedisplay circuit 25. In some embodiments one side of the PCB isconfigured for mounting components, and a second side of the PCB isconfigured with solder pads.

In some embodiments the sensor plates 5 are arranged on a first PCB. Insome embodiments the interconnection circuitry is arranged on a secondPCB. In some embodiments the first PCB is bonded to the second PCB.

In some embodiments there are solder pads on the sensor plate board 40that are complementary with solder pads on an interconnection board. Insome embodiments the sensor plate board 40 and the interconnection boardmay be stacked on top of one another and bonded to each other. In someembodiments the bonding agent that bonds the two PCBs together may besolder. In some embodiments solder paste may be used to bond two PCBstogether. In some embodiments, they may be bonded together with solderand the process to bond them together may be standard SMT (surface mounttechnology) processes. The standard SMT process may include using astencil to place solder paste in the desired locations. The SMT processmay include placing one PCB on top of another. In some embodiments pinsmay be used to ensure proper alignment of the two PCBs. In someembodiments the final step of the SMT process may involve running thestacked PCBs through a reflow oven.

In some embodiments the sensor plates 5, shield, and circuitry areplaced on a single PCB. In some embodiments a six-layer PCB is used. Insome embodiments the bottom layer, which is the sixth layer, of the PCBis configured with the sensor plates 5. The fifth layer may be an activeshield. The top four layers may connect the balance of the circuitry.

In some embodiments the sensor plates 5, shield, and circuitry areplaced on a single PCB. In some embodiments a four-layer PCB is used.First and second layers of the PCB are configured with interconnectioncircuitry. In some embodiments the bottom layer, which is the fourthlayer, of the PCB is configured with the sensor plates 5. The thirdlayer may be an active shield.

The PCB can be made from a variety of suitable materials, such as, forexample, FR-4, FR-406, or more advanced materials used in radiofrequency circuits, such as Rogers 4003C. Rogers 4003C, and otherradio-frequency-class PCB substrates, may offer improved performanceacross a broader temperature and humidity range.

As used herein, the term “module” can describe any given unit offunctionality that can perform in accordance with one or moreembodiments of the present invention. For example, a module might byimplemented using any form of hardware or software, or a combinationthereof, such as, for example, one or more processors, controllers 60,ASICs, PLAs, logical components, software routines, or other mechanisms.

Different processes of reading a capacitance and converting it to adigital value, also known as a capacitance-to-digital conversion, arewell-described in the prior art. The many different methods are notdescribed here, and the reader is referred to the prior art for detailsabout different capacitance-to-digital converter methods. Someembodiments use a sigma-delta capacitance-to-digital converter, such asthe one that is built into the Analog Devices AD7747 integrated circuit.Some embodiments use a charge-sharing method of capacitance-to-digitalconversion.

In some embodiments the voltage regulator 26 may comprise the ADP150-2.8from Analog Devices, or the NCP702 from ON Semiconductor, which providevery low noise. In some embodiments, the controller 60 may comprise theC8051F317 from Silicon Laboratories, or any of many othermicrocontrollers.

Detecting obscured features 3 can require a high degree of accuracy, andmay require more accuracy than the capacitance-to-digital converter 21may be able to provide, if the native capacitance-to-digital converter21 sensor readings are used alone. Native sensor readings are the rawvalues read from the capacitance-to-digital converter 21; they are thedigital output of the capacitance-to-digital converter 21.

Some embodiments perform native reads multiple times, and combine theresults of the multiple native reads, to create a reading. Someembodiments perform native reads multiple times, and combine the resultsof the multiple native reads, using a different configuration for two ormore of the native reads to create a reading. Some embodiments performnative reads multiple times, and sum or average the results of themultiple native reads, to create a reading. In some embodiments thisimproves the signal-to-noise ratio. Each native read may involve readingone sensor plate 5. A native read could also involve reading a pluralityof sensor plates 5, if multiple sensor plates 5 are multiplexed to thecapacitance-to-digital converter 21. In some embodiments multiple nativereads are combined to create a reading.

Summing or averaging multiple native reads may improve thesignal-to-noise ratio, but may not reduce the effect of non-linearitiesin the capacitance-to-digital converter 21. The idealcapacitance-to-digital converter 21 is perfectly linear, which meansthat its native sensor readings increase in direct proportion to anincrease in the capacitance being sensed. However, manycapacitance-to-digital converters 21 may not be completely linear, suchthat a change in the input capacitance does not result in an exactlyproportional increase in the native reading. These non-linearities maybe small, but when a high degree of accuracy is desired it may bedesirable to implement methods that reduce the effects of thenon-linearities.

In some embodiments, the ill effects of the non-linearities may bemitigated by summing multiple native reads, using a slightly differentconfiguration for each of the native reads. Some embodiments performnative reads using two or more different configurations.

For example, the bias current is one parameter that can be altered tocreate different configurations. The bias current could be set tonormal, or normal +20%, normal +35%, or normal +50%. Different biascurrents produce different native sensor readings, even if all otherfactors remain constant. Since each native reading has a differentvalue, presumably each native reading may be subject to differentnon-linearities. Presumably summing or averaging sensor readings thatare subject to different non-linearities may cause the non-linearitiesto partially cancel each other out, instead of being summed ormultiplied.

In some embodiments there are two separate and independentcapacitance-to-digital converters 21. In some embodiments each of themmay have different non-linearities. Using both of thecapacitance-to-digital converters 21, using the first converter for someof the reads and using the second converter for some of the reads, maymitigate the effect of any single non-linearity.

Some embodiments perform native reads on each of the sensor plates 5using each of twelve different configurations.

After completing the sensor readings, in some embodiments, two differentcalibration algorithms may be performed: first an individual-platecalibration that adjusts for individual sensor plate 5 variations, andsecond a surface material calibration that adjusts the sensor readingsso that they are tuned to the surface density/thickness. Otherembodiments may only use one of the two calibration algorithms. Someembodiments may use other calibration algorithms. In some embodimentsthe calibration algorithms are performed by a calibration module.

In some embodiments, individual plate calibration is employed first.With individual plate calibration, each sensor plate 5 may have its ownindividual calibration value. In some embodiments, after the sensorreadings are taken, an individual plate calibration value is added to,or subtracted from, each of the sensor readings. Other embodiments mayuse multiplication, division, or other mathematical functions to performthe individual plate calibration. In some embodiments, the individualplate calibration value is stored in non-volatile memory. Individualplate calibration compensates for individual sensor plate 5irregularities, and is used to compensate for these irregularities. Insome embodiments it is presumed that after performing individual platecalibration that the sensor readings will presumably have the samecalibrated values, if the sensor plate sensor readings are taken whilethe obscured feature detector 1 is on the surface 2 that is similar tothe surface 2 the obscured feature detector 1 was calibrated on. Forexample, if sensor readings are performed on ½″ sheetrock 2, without anyobscured features 3 present, and the individual calibration values werecreated for ½″ sheetrock 2, then after performing individual platecalibration, it is presumed that all the sensor readings would becorrected to a common value. If sensor readings are performed on athicker material (such as ⅝″ sheetrock 2), a thinner material (such as⅜″ sheetrock 2) or a different material (such as ¾″ plywood) then theremay be some error in the values. Surface material calibration may helpcorrect this error.

In some embodiments surface material calibration may be used.

In some embodiments, after calibrating the sensor plate sensor readingsthe obscured feature detector 1 decides if an obscured feature 3 ispresent. In some embodiments the lowest sensor plate reading issubtracted from the highest sensor plate reading. If the difference isgreater than a threshold value then a determination is made that anobscured feature 3 is present.

If it is determined that no obscured features 3 are present, then all ofthe indicators 6 may be deactivated. If an obscured feature 3 is presentthen the obscured feature detector 1 begins the process of determiningthe position(s) and width(s) of the obscured feature(s) 3.

In some embodiments pattern matching may be employed to determine whichLEDs to activate. In some embodiments a pattern matching module is usedto determine the locations of the obscured features 3. The patternmatching module compares the calibrated and scaled sensor readings fromthe sensor plates 5 to several predetermined patterns. The patternmatching module determines which predetermined pattern best matches thesensor readings. Then the set of indicators 6 that corresponds to thebest matching pattern is activated. Additional details about patternmatching are discussed in the prior art, such as in U.S. Pat. No.8,884,633. Those details will not be repeated here; instead the readeris encouraged to refer to them directly.

In some embodiments the obscured feature detector 1 comprises a singlecapacitance-to-digital converter 21. In some embodiments the sensorplates 5 may be individually connected to the capacitance-to-digitalconverter 21. In some embodiments the sensor plates 5 may beindividually connected to the capacitance-to-digital converter 21 viathe multiplexer 18. In some embodiments more than one sensor plate 5 maybe connected to the capacitance-to-digital converter 21 at a time. Insome embodiments multiple adjacent sensor plates 5 may be electricallyconnected to the capacitance-to-digital converter 21. In someembodiments multiple non-adjacent sensor plates 5 may be connected tothe capacitance-to-digital converter 21. The use of a multiplexer 18 toconnect sensor plates 5 to a single capacitance-to-digital converter 21may improve sensor plate 5 to sensor plate 5 consistency of the sensorreadings, because the sensor readings from each of the sensor plates 5may be equally affected by variations to the capacitance-to-digitalconverter 21. Factors that may affect the sensor readings from thecapacitance-to-digital converter 21 may include, but are not limited to,process variations, temperature variations, voltage variations,electrical noise, aging, and others.

In some embodiments, the sensor plate traces 35 are routed such thateach of the sensor plate traces 35 has substantially equal capacitance,resistance, and inductance. In some embodiments it is desirable for eachof the sensor plate traces 35 to have the same electrical properties, sothat each of the sensor plates 5 will respond equivalently to the samedetected object(s).

In some embodiments each of the sensor plate traces 35 from thecapacitance-to-digital converter 21 to each of the sensor plates 5 hassubstantially the same length. In some embodiments two or more of thesensor plate traces 35 from the capacitance-to-digital converter 21 tothe sensor plates 5 have substantially the same length. In someembodiments sensor plate traces 35 with substantially the same lengthmay have more equivalent capacitances, inductances, and resistances.Equal length sensor plate traces 35 may offer enhanced performancebecause they may improve the uniformity of the sensor readings, suchthat the sensor plates 5 respond more equivalently to the same detectedobjects, and may provide more immunity from environmental conditions,such as temperature and humidity.

In some embodiments each of the sensor plate traces 35, which compriseselectrically conductive paths, has substantially the same width. In someembodiments, both the width and the length of each of the sensor platetraces 35 are substantially equivalent. In some embodiments the sensorplate traces 35 will have more than one segment. For example, a firstsegment of the traces may route the sensor plate traces 35 from acapacitance-to-digital converter 21 to a via. The via may take thesensor plate trace 35 to a different layer of the PCB, where there maybe a second segment of the sensor plate trace 35. In some embodimentsall of the sensor plate traces 35 will have the same length and width,in each segment, as the other traces in that segment. In someembodiments two or more of the sensor plate traces 35 will have the samewidth throughout a first segment. In some embodiments two or more of thesensor plate traces 35 will have the same width throughout a secondsegment. In some embodiments two or more of the sensor plate traces 35will have the same length throughout a first segment. In someembodiments two or more of the sensor plate traces 35 will have the samelength throughout a second segment.

In some embodiments the sensor plate traces 35 comprise multiplesegments. In some embodiments a segment of a sensor plate trace 35 maybe the wire bonds that are within the package of an integrated circuitthat route the signals from the piece of silicon to the pins of theintegrated circuit package. In some embodiments a segment of a sensorplate trace 35 may comprise a layer of copper on a first layer of a PCB.In some embodiments a segment of a sensor plate trace 35 may comprise alayer of copper on a second layer of a PCB.

In some embodiments the capacitance-to-digital converter 21 will readthe sum of the capacitance on the sensor plates 5 and the capacitance onthe sensor plate traces 35. In some embodiments, only detecting thesensor readings on the sensor plates 5, and not detecting the sensorplate traces 35, may be preferable. However, because the sensor plates 5and sensor plate traces 35 are electrically coupled, a means of ensuringstable and uniform capacitance on the sensor plate traces 35 may bedesired. For example, it may be desirable to configure the sensor platetraces 35 so that their capacitance is uniform and stable. Consequently,it may be preferred for the sensor plate traces 35 to be configured sothat the sensor plate traces 35 do not change. In some embodiments itmay be preferred that the sensor plate traces 35 do not change relativeto each other, such that any change in the capacitance on one sensorplate trace 35 is reflected in each of the sensor plate traces 35.

In some embodiments it may be advantageous to shield the sensor platetraces 35. Sensor plate trace shielding may protect the sensor platetraces 35 from external electromagnetic fields. In some embodimentsshielding the sensor plate traces 35 may also advantageously provide amore consistent environment for the sensor plate traces 35 by helping toensure that each of the sensor plate traces 35 has an environment thatis similar to each of the other sensor plate traces 35.

In some embodiments each of the sensor plate traces 35 from thecapacitance-to-digital converter 21 to each of the sensor plates 5 hassubstantially the same surroundings. In some embodiments the sensorplate traces 35 are routed sufficiently far apart so that capacitive andinductive coupling between the sensor plate traces 35 is minimized, andmay improve consistency because each of the sensor plate traces 35 mayhave surroundings that are more similar to the other sensor plate traces35. In some embodiments each of the sensor plate traces 35 is shieldedon one or both sides with an active shield trace.

In some embodiments a user may be electrically coupled to the sensingcircuit 27. In some embodiments the quality of the sensor readings isincreased when an electrically conductive point of the sensing circuit27 is coupled to the user. Electrically coupling the user to the sensingcircuit 27 may provide a stationary voltage level for the sensingcircuit 27 and may result in higher quality sensor readings that havehigher sensitivity. For example, a prior art obscured feature detectorthat drives the sensor plates 5 with a 3.0V may in reality only drivethe sensor plates 5 with a 3.0V signal relative to ground. However, ifthe ground is floating, then driving the sensor plates 5 with 3.0V couldresult in a 1.5V signal on the sensor plates 5 and a −1.5V signal on theground. In some embodiments the quality of the sensor readings is notincreased when an electrically conductive point of the sensing circuit27 is coupled to the user.

In some embodiments electrically coupling the user to the sensingcircuit 27 may result in higher absolute voltage swings on the sensorplates 5, which may be due in part to the sensing circuit 27 being heldat a stable level. In some embodiments electrically coupling the user tothe sensing circuit 27 may also result in sensor readings that are moreconsistent.

In some embodiments the user is electrically coupled to the ground ofthe sensing circuit 27, as shown in FIG. 4. In some embodiments the useris electrically coupled to the voltage source of the sensing circuit 27.In some embodiments the user is electrically coupled to a differentelectrically conductive point of sensing circuit 27.

In some embodiments the hand of the user may be electrically coupled tothe sensing circuit 27 by making direct contact with the sensing circuit27. In some embodiments an electrically conductive material, such as awire, may electrically couple the hand of the user to the sensingcircuit 27. In some embodiments the button, which the user would need totouch to activate the obscured feature detector 1, may comprise anelectrically conductive material which may be electrically coupled tothe sensing circuit 27. In some embodiments the button may comprisealuminum or another electrically conductive material such as tin-platedsteel. In some embodiments an aluminum button may be anodized, which mayprovide pleasing cosmetics.

In some embodiments the housing 19 (see FIG. 2) of the obscured featuredetector 1 may comprise an electrically conductive material, such as anelectrically conductive plastic. In some embodiments only a portion ofthe housing 19 may comprise electrically conductive plastic. Theelectrically conductive housing, or a portion of the electricallyconductive housing, may be coupled to an electrically conductive pointin the sensing circuit 27, thereby coupling the user to the sensingcircuit 27.

In some embodiments mixing carbon black with the plastic resin mayprovide electrically conductive properties. Many thermoplastics,including polypropylene and polyethylene, become electrically conductivewhen a carbon black is mixed into the plastic resin. In some embodimentsthe conductivity increases as the concentration of carbon black isincreased, advantageously making it possible to control the conductivityof the plastic. In some embodiments a plastic with a conductivity thatis less than about 25,000 ohms-cm provides sufficiently highconductivity to effectively couple the user to the sensing circuit 27.In some embodiments a higher degree of conductivity may be desired. Insome embodiments a lower degree of conductivity may be desired. In someembodiments it is advantageous for the user to be coupled to the sensingcircuit by a path with less than about 50 mega-ohms.

In some prior art obscured feature detectors, a change in the positionof the hand of the user can cause a change in the sensor readings. Thismay occur in some prior art obscured feature detectors because the handmay form a portion of the path between the sensor plates 5 and ground.As a result, a change in hand position can cause a change in the sensorreadings of the sensor plates 5. Disadvantageously, this may reduce theaccuracy of the sensor readings.

If it were possible for the size and position of the hand of the user tobe constant, it may be possible to do a calibration adjustment tomathematically remove the effect of the hand of the user from the rawsensor readings. However, in practice this may not be feasible. Inpractice the size, shape, and position of hands of different users mayvary too much to make a calibration adjustment practically possible.

To improve performance in light of the aforementioned issues, in someembodiments a conductive hand guard may be positioned between the handof the user and the sensor plates 5. In some embodiments the hand guardmay be grounded to the sensing circuit 27, as illustrated in FIG. 4.

FIG. 5 is a diagram of the controller 60, according to one embodiment.The controller 60 includes a processor 61, a clock 62, random accessmemory (RAM) 64, a non-volatile memory 65, and/or anothercomputer-readable medium. The non-volatile memory 65 may include aprogram 66 (e.g., in the form of program code or computer-executableinstructions for performing operations) and calibration tables 68. Inoperation, the controller 60 may receive the program 66 and maysynchronize the functions of the capacitance-to-digital converter 21 andthe display circuit 25 (see FIG. 4). The non-volatile memory 65 receivesand stores the program 66 as well as look-up tables (LUT) andcalibration tables 68. The program 66 can include a number of suitablealgorithms, such as, for example, an initialization algorithm, acalibration algorithm, a pattern-matching algorithm, a multiplexingalgorithm, a display management algorithm, an active sensor activationalgorithm, and a non-active sensor management algorithm.

FIG. 6 is a cross-sectional view of an obscured feature detector,according to one embodiment, including a housing, with light pipes and abutton, and a PCB. In some embodiments, as shown in FIG. 6, a housing 19comprises an upper housing, an on-off switch 24, a handle 14, aplurality of light pipes 8, and a power supply compartment. In someembodiments a conforming core may be configured to flexibly couple thehousing 19 to a sensor plate board 40. In some embodiments the sensorplate board 40 is a multi-layered PCB with a top layer 44, a secondlayer 43, a third layer 42, and a bottom layer 41. In some embodimentsthe sensor plate board 40 is a multi-layered PCB that couples acapacitance-to-digital converter 21, a display circuit 25, and acontroller 60, as described above with reference to FIG. 4. In someembodiments, the housing 19 comprises plastic. In some embodiments, thehousing 19 comprises ABS plastic. In some embodiments a conductive handguard 56 shields the user's hand from the sensor plate board 40. In someembodiments the hand guard 56 is connected to the ground of a sensingcircuit.

In some embodiments, the handle 14 comprises a gripping surface. In someembodiments a portion of the gripping surface comprises an elastomerthat makes the handle 14 easier to grip. The handle 14 is preferablypositioned so that the user's hand does not obscure a view of theindicators 6 when grasping the handle 14. In some embodiments, the powersupply compartment comprises a cavity for holding a suitable powersupply, such as batteries, and a battery cover for accessing thecompartment.

In some embodiments the hand guard 56 may be configured so that thereare no significant straight-line paths between the sensor plates and theuser's hand. In some embodiments the housing 19 may be composed of anelectrically conductive material which may comprise the hand guard 56.In some embodiments the conductive layer of material of the hand guard56 may be a layer of conductive plastic. In some embodiments theconductive layer of material of the hand guard 56 may be a layer of adifferent conductive material, such as a conductive paint. In someembodiments the conductive layer of material of the hand guard 56 may bea sheet of metal that is hidden within the housing 19. In someembodiments the hand guard 56 may comprise segments of extruded aluminumthat are soldered to the PCB. In some embodiments the hand guard 56 maycomprise tin-plated steel, which may provide for quick, easy andreliable solder joints. In some embodiments an entire layer of a PCB maycomprise the hand guard 56, such as the top layer of the PCB (printedcircuit board). In some embodiments only a portion of a layer of a PCBmay comprise the hand guard 56, because in some embodiments it may notbe necessary to for the hand guard 56 to comprise an entire layer. Forexample, a ring around the outside of a PCB may be an effective handguard 56.

In some embodiments the hand guard 56 is configured to minimize aneffect of a size and position of the hand. In some embodiments the handguard 56 is positioned so that it is near the hand because in someembodiments it may be most effective when it is nearest to the hand. Insome embodiments the hand guard 56 may be electrically coupled to theground of a sensing circuit 27 (see FIG. 4). In some embodiments thehand guard 56 may be coupled to the voltage of the sensing circuit 27.In some embodiments a different electrically conductive point of thesensing circuit 27 may be electrically coupled to the hand guard 56. Insome embodiments an electrical wire comprises the electrical pathbetween the hand guard 56 and the sensing circuit 27.

In prior art obscured feature detectors a set of identical sensor plates105 are typically arranged in a linear fashion, such as is shown inFIGS. 7, 8, 9, and 10. FIG. 7 is a prior art obscured feature detector101 placed on a comparatively thinner surface 12. FIG. 8 is the priorart obscured feature detector 101 placed on a comparatively thickersurface 13. FIG. 9 shows a side view of the prior art obscured featuredetector 101, illustrating primary sensing field zones 15, 16, 17 forseveral sensor plates 105, including sensor plates A, B, C, D, E. FIG.10 shows an elevation view of a bottom surface of the prior art obscuredfeature detector 101, illustrating the primary sensing field zones 15,16, 17 for sensor plates A, B, C, D, E.

Referring generally and collectively to FIGS. 7-14, each of the sensorplates 105 performs a sensor reading of the surface 2. The sensorreadings are then compared. The sensor plates 105 that have the highestsensor readings are interpreted to be the locations of obscuredfeatures. However, as shown in FIGS. 7 and 8, the sensor plates 105 thatare near the ends of the group may not respond to obscured features inthe same manner as the sensor plates 105 that are near the center. Thisissue may be particularly evident when the prior art obscured featuredetector 101 is moved from the thinner, or less dense, surface 12, to athicker, or more dense, surface 13.

FIG. 7 shows representative sensor readings of the prior art obscuredfeature detector 101 that is placed on the relatively thinner surface12. The relatively thinner surface 12 could be 0.375-inch-thicksheetrock. FIG. 8 shows representative sensor readings of the prior artobscured feature detector 101 that is placed on a relatively thickersurface 13. The relatively thicker surface 13 could be 0.625-inch-thicksheetrock.

In FIG. 7, the prior art obscured feature detector 101 is placed on therelatively thinner surface 12. Each of the sensor plates 105 may have acalibration adjustment so that each has a calibrated reading of, forexample, 100. If this same prior art obscured feature detector 101 isthen moved to another surface 13 that is thicker, or to a surface thathas a higher dielectric constant, the sensor readings would change. Animage of the same prior art obscured feature detector 101 on the thickersurface 13 is shown in FIG. 8. Ideally, each of the sensor plates 105 onthe thicker surface 13 would have similar sensor readings to each other,because they are all on the same thicker surface 13, with no obscuredfeatures present. However, it may be observed that the sensor readingsof the sensor plates 105 near the ends may see a larger reading increasethan the sensor plates 105 near the center. In FIG. 8, it may be seenthat the sensor plates 105 near the center have sensor readings of 200,but the sensor plates 105 at the ends have sensor readings of 250.

In the prior art obscured feature detector 101 of FIG. 8, and otherprior art obscured feature detectors, the sensor plates 105 that are atthe ends are alone in creating electric fields 9 that extend beyond theedges of the group of sensor plates 105. As a result, the sensor plates105 near the end may respond with a disproportionately higher readingwhen placed on a thicker surface 13. Disadvantageously, the controller60 may have difficulty determining if the elevated sensor readings aredue to the presence of an obscured feature, or due to the prior artobscured feature detector 101 being placed on the thicker surface 13.The disclosed embodiments may address these and other challenges.

FIG. 9 illustrates the field lines for the prior art obscured featuredetector 101 of FIGS. 7 and 8. FIG. 9 shows a group of sensor plates 105and also shows a two-dimensional representation of the field lines foreach of the sensor plates 105. The field lines are shown forillustrative purposes and are a representation of the actual sensingfield. The field lines drawn are equipotential electric field lines.However, this drawing does not limit the scope of the disclosure to thistype of field alone. Vector electric field lines or magnetic field linescould have been illustrated in the drawing and are within the scope ofthe disclosure. The sensing field may be an electric field, a magneticfield, or an electromagnetic field, which is a combination of anelectric field and a magnetic field.

In FIG. 9 there are thirteen sensor plates 105. All of the sensor plates105 may be driven with the same signal simultaneously, while one sensorplate 105 at a time is sensed. Because the sensor plates 105 are drivensimultaneously, with the same signal, the sensing field is defined bythe field created by the group of sensor plates 105, as illustrated inFIG. 9. An active shield plane is not illustrated in the figure, but anactive shield may contribute to the sensing field in some embodiments.Five of the sensor plates 105 are labeled A, B, C, D, E. The field linesemanating from sensor plate E are primarily parallel to sensor plate E.However, the field lines emanating from sensor plate A are not veryparallel to sensor plate A. Because the field lines do not have similardirection and strength at each point within the primary sensing fieldzone the sensor plates A and E do not have similar sensing fields withintheir primary sensing field zones.

In contrast, sensor plate D and sensor plate E have similar primarysensing field zones because the volume of the sensing field where theyare able to sense effectively and the sensing field within that primarysensing field zone are similar. The sensing fields within a primarysensing field zone are similar if the direction of the sensing field andstrength of the sensing field are similar at each point within theprimary sensing field zone.

FIG. 10 illustrates the same concept from a different angle orperspective. In FIG. 10 the five sensor plates 105 are again labeled A,B, C, D, E. The approximate primary sensing field zones for each of thesensor plates 105 are highlighted. On the two-dimensional drawing ofFIG. 10, the primary sensing field zone 15 for sensor plate A isindicated by the drawing of the sensing field lines for sensor plate A.On the two-dimensional drawing of FIG. 10, the primary sensing fieldzone 16 for sensor plate B is indicated by the drawing of sensing fieldlines for sensor plate B. On the two-dimensional drawing of FIG. 10, theprimary sensing field zone 17 for sensor plate C is indicated by thedrawing of sensing field lines for sensor plate C.

FIGS. 9 and 10 illustrate the primary sensing field zone with atwo-dimensional drawing. However, in reality a three-dimensional primarysensing field zone may exist. There may be a three-dimensional zone foreach sensor plate 105 that comprises the primary sensing field zone foreach given sensor plate 105. In contrast to the prior art embodiment ofFIGS. 9 and 10, in some embodiments of the present disclosure the sensorplates 105 may have an equivalent primary sensing field zone. Eachsensor plate 105 in a group that has an equivalent primary sensing fieldzone may have an equivalent response to change in surfaces. Thisdisclosure illustrates some configurations wherein each sensor plate 105in a group may have an equivalent primary sensing field zone. In someembodiments each sensor plate 105 with a similar primary sensing fieldzone may have a similar change in sensor readings in response to achange in the detected surface.

FIG. 11 is a flow diagram of a method 200 of detecting an obscuredfeature behind a surface, according to one embodiment. A firstoperation, as illustrated in the flow diagram in FIG. 11, may be toinitialize a detector 202, which may involve running an initializationalgorithm. The detector may be according to one of the embodimentsdescribed herein. After initialization, the sensor plates may be read204. In some embodiments each of the sensor plates may be read multipletimes, each time using a different configuration. The differentconfigurations may comprise different drive currents, different voltagelevels, different sensing thresholds, or other different configurationparameters. Each of these readings of the sensor plates may be referredto as native readings. In some embodiments multiple native readings maybe added together to comprise a reading. In some embodiments there maybe a separate reading for each sensor plate.

In some embodiments, each of these readings has a calibration 206adjustment performed that is achieved by adding a predeterminedcalibration value to each reading. In some embodiments, aftercalibration, the readings for each of the sensor plates would be thesame if the detector were to be placed on a uniform surface.

In some embodiments, the largest sensor plate reading is compared 208 tothe lowest sensor plate reading. The difference is then compared 208 toa threshold value. In some embodiments, if the difference is less than apredetermined threshold value, then all of the indicators may be turnedoff 210, to indicate that no stud is present. If the difference islarger than a predetermined threshold value, then a determination may bemade as to which indicators to activate. In certain embodiments, thereadings may be scaled 212 to a predetermined range, which may involvesetting the lowest value to a number such as 0 and scaling the largestreading to a value such as 100. Then all of the intermediate valueswould be scaled proportionately. The scaled readings may then becompared 214 to predetermined patterns which are scaled in a similarfashion.

In some embodiments there may be a set of predetermined patterns. Theset of predetermined patterns may correspond to different combinationsof hidden features that the detector may encounter. For example, the setof predetermined patterns may correspond to different positions for asingle stud. In some embodiments, the set of predetermined patterns mayinclude positional combinations of two studs. A pattern matchingalgorithm may be employed to determine which predetermined pattern bestmatches the reading pattern. The detector may then activate 216 theindicators that correspond to the best matching predetermined pattern.

In other embodiments, after calibrating the sensor plate readings, adetermination is made if an obscured feature is present. The lowestsensor plate reading may be subtracted from the highest sensor platereading. If the difference is greater than a threshold value, then adetermination is made that an obscured feature is present. If it isdetermined that no obscured features are present, then all of theindicators may be deactivated. If an obscured feature is present then aprocess may begin to determine position(s) and/or width(s) of theobscured feature(s). In some embodiments, all of the current sensorplate readings may be scaled such that the lowest reading is scaled to apredetermined value (such as 0) and the maximum reading is scaled to asecond predetermined value (such as 100). All intermediate values may bescaled proportionately. Scaled readings may be easier to compare to aset of predetermined patterns.

FIG. 12 is a presently available obscured feature detector 1200 having asensor plate group arranged in a typical plate configuration. As shown,the obscured feature detector 1200 may comprise three or more sensorplates 1205, a common plate 1202, and an active shield plate 1223.

The sensor plates 1205 of the obscured feature detector 1200 arearranged linearly to form a sensor array 1207. As shown, the sensorplates 1205 may have the same geometry and be evenly spaced. Each sensorplate 1205 has an internal border extending along at least a portion ofan internal border of one or more other sensor plates 1205, and anexternal border disposed at an outer perimeter of the sensor array 1207.The linear sensor array includes two end sensor plates 1210, 1212 and atleast one non-end sensor plate 1214.

Each sensor plate 1205 is configured to take a sensor reading thatvaries based on a proximity of the sensor plate 1205 to one or moresurrounding objects and on a material property of each of the one ormore surrounding objects. To facilitate the sensor reading, an area ofeach sensor plate 1205 may form a first end of a corresponding electricfield.

The common plate 1202 may form a second end of the correspondingelectric field of each sensor plate 1205. The common plate 1202 has alength 1220 extending along a length 1222 of the sensor array, such thatthe common plate 1202 extends along one external border of each of thesensor plates 1205. As shown, the common plate 1202 extends beyond anentire linear dimension of the sensor array 1207. Common plates ofpresently available plate configurations are at least 17 mm longer thanthe sensor array, whether due to housing size or shape, shieldingconfigurations, or other reasons. The electric fields of the end sensorplates formed with such longer common plates are non-uniform incomparison to the electric fields formed by non-end sensor plates withsuch longer common plates.

FIG. 13 is a bottom elevation view of an obscured feature detector 1300having sensor plate cluster 1301 arranged in an improved plateconfiguration with a shortened common plate 1302. As shown, the obscuredfeature detector 1300 may comprise three or more sensor plates 1305, theshortened common plate 1302, and an active shield plate 1323.

The sensor plates 1305 in the embodiment shown are arranged linearly toform a sensor array 1307. As shown, the sensor plates 1305 may have thesame geometry and be evenly spaced. In other embodiments, the sensorplates 1305 may vary in size and/or shape, and may be spaced differentlybased on the position of the sensor plate 1305 in the sensor array 1307.The linear sensor array 1307 includes two end sensor plates 1310, 1312and at least one non-end sensor plate 1314.

Each sensor plate 1305 is configured to take a sensor reading thatvaries based on a proximity of the sensor plate 1305 to one or moresurrounding objects and on a material property of each of the one ormore surrounding objects. To facilitate the sensor reading, an area ofeach sensor plate 1305 may form a first end of a corresponding electricfield.

The shortened common plate 1302 may form a second end of thecorresponding electric field of each sensor plate. The shortened commonplate 1302 has a length 1320 extending along a length 1322 of the sensorarray 1307 such that the shortened common plate 1302 extends along thesensor array 1307. In some embodiments, the shortened common plate 1302may not extend along one or both of the end sensor plates 1310, 1312. Insome embodiments the length 1320 of the shortened common plate 1302 isless than the length of the length of the sensor plate cluster 1301. Insome embodiments the sensor plate cluster 1301 includes the sensorplates 1305. In some embodiments the sensor plate cluster 1301 includesthe sensor plates 1305 and an active shield plate 1323. In someembodiments the sensor plate cluster 1301 also includes a common plate1302 and may also include circuitry mounted on the side of the sensorplate cluster 1301 that is opposite the sensor plates 1305. In someembodiments the length 1320 of the shortened common plate 1302 is lessthan the length of the sensor array 1307. In some embodiments the length1320 of the shortened common plate 1302 is less than the length of thelength of the sensor plate cluster 1301. In some embodiments the lengthof the common plate is less than the collective length of the sensorplates 1305 and the active shield plate 1323. In the embodiment shown,the shortened common plate 1302 is centered along the sensor array 1307.In some embodiments the shortened common plate 1302 may be off-centered.

The active shield plate 1323 is disposed between and separates thesensor plates 1305 and the shortened common plate 1302. In theembodiment shown, the active shield plate 1323 surrounds the shortenedcommon plate 1302 along three sides. In other embodiments the activeshield plate 1323 may only run along the length 1320 of the shortenedcommon plate 1302. However, having the active shield plate 1323 surroundthe common plate may decrease the complexity of manufacturing.

In some embodiments, one sensor plate 1305 may be sensed at a time. Insome embodiments when one sensor plate 1305 is sensed, all of the sensorplates 1305, including the active shield plate 1323, are driven with thesame signal as the sensed sensor plate 1305. The sensor array 1307, plusthe active shield plate 1323, when driven together may push the fieldlines of the corresponding electric field deeper into the sensed surfacethan may be possible if just a single sensor plate 1305 was driven. Insome embodiments this allows field lines from a single sensor plate 1305to penetrate more deeply, and allows a single sensor plate 1305 to sensemore deeply, than may be possible if a single sensor plate 1305 weredriven alone.

FIG. 14 illustrates the electric fields created by the prior art plateconfiguration of the obscured feature detector 1200 of FIG. 12. Eachsensor plate 1205 is configured to provide a primary coupling area 1402,1412 to form a first end of a corresponding electric field 1406, 1408.Further, the common plate 1202 is configured to provide a correspondingprimary coupling area 1404, 1414 to correspond to a sensor plate 1205and form a second end of the corresponding electric field 1406, 1408 ofthat sensor plate 1205.

The primary coupling area 1402, 1412 is the area of the sensor plate1205 where the electric field 1406, 1408 primarily couples. In theillustrated prior art, the primary coupling area 1402 of the end sensorplate 1210 is on a line 1420 with the corresponding primary couplingarea 1404 of the common plate 1202. Similarly, the primary coupling area1404 of the non-end sensor plate 1214 is on a line 1422 with thecorresponding primary coupling area 1414 of the common plate 1202. Asshown, the line 1420 of the primary coupling area 1402 of the end sensorplate 1210 to the corresponding primary coupling area 1404 of the commonplate 1202 is approximately parallel with the line 1422 of thecorresponding primary coupling area 1404 of the non-end sensor plate1214 to the corresponding primary coupling area 1414 of the common plate1202.

As shown, the electric field 1406 formed from the end sensor plate 1210in this configuration has a different geometry than the electric field1408 formed from the non-end sensor plate 1214. The electric fieldsgenerated by surrounding sensor plates 1205 affect each other sensorplate 1205. The non-uniform electric field 1406 is a result of the endsensor plate 1210 not having sensor plates 1205 along both sides. Thenon-uniformity of the electric field 1406 may result in an inaccuratedetection or a missed detection of obscured features. For example, theelectric field 1406 generated by the end sensor plate 1210 may penetratemore broadly into a surface than the electric field 1408 generated bythe non-end sensor plate 1214. Because of the different sensing areas,the end sensor plate 1210 may falsely identify an obscured feature.

FIG. 15 illustrates the electric fields 1506, 1508 created between anend sensor plate 1310 and a non-end sensor plate 1314 in the plateconfiguration of the obscured feature detector 1300 of FIG. 13. Primarycoupling areas (e.g., 1502, 1512) may couple the sensor plates 1305 tothe shortened common plate 1302. Each of the sensor plates 1305 isconfigured to provide a primary coupling area (e.g., 1502, 1512) to forma first end of a corresponding electric field. The common plate 1302 isconfigured to provide corresponding primary coupling areas (e.g., 1504,1514) that each correspond to a sensor plate 1305 and forms a second endof the corresponding electric field of that sensor plate 1305.

For example, as shown, the end sensor plate 1310 is configured toprovide the primary coupling area 1502 and the non-end sensor plate 1314is configured to provide the primary coupling area 1512. The commonplate 1302 is configured to provide a corresponding primary couplingarea 1504 that corresponds to the primary coupling area 1502 of the endsensor plate 1310 and a corresponding primary coupling area 1514 thatcorresponds to the primary coupling area 1512 of the non-end sensorplate 1314.

As illustrated, the electric fields 1506, 1508 couple the primarycoupling areas 1502, 1512 of the sensor plates 1305 to the correspondingprimary coupling areas 1504, 1524 of the common plate 1302. The primarycoupling area 1502 of the end sensor plate 1310 is on a first line 1520with the corresponding primary coupling area 1504 of the common plate1302. Further, the primary coupling area 1512 of the non-end sensorplate 1314 is on a second line 1522 with the corresponding primarycoupling area 1514 of the common plate 1302.

To achieve similar electric fields, the first line 1520 and the secondline 1522 between the coupling areas of the sensor plates 1305 and thecommon plate 1302 are non-parallel. The electric fields generated byneighboring sensor plates 1305 affect each other sensor plate 1305.Because the end sensor plate 1310 only has one neighboring sensor plate1305, the electric field 1506 would naturally travel a greater distancethan the electric field 1508 of the non-end sensor plate 1324. As shownin FIG. 14, the path of the greater distance may extend beyond theobscured feature detector. In contrast, as shown In FIG. 15, theshortened common plate 1302 pulls the electric field 1506 into nearalignment with the electric field 1508. This may be because the sizingand placement of the shortened common plate 1302 causes the electricfield 1506 from the end sensor plate 1310 to have more similarity to theelectric field 1508 to the non-end sensor plate 1314, as compared toprior art obscured feature detectors.

In some embodiments the electric field 1506 that corresponds to the endsensor plates 1310 has a similar size, shape, direction, and/or geometryas the electric field 1508 that corresponds to the non-end sensor plate1314. In some embodiments the electric fields that correspond to each ofthe sensor plates 1305 have the same size, shape, direction, and/orgeometry as each of the other sensor plates 1305. In some embodiments,the electric fields that correspond to each of a group of sensor plates1305 have the same size, shape, direction, and/or geometry.

In some embodiments similar electric field size, shape, direction,and/or geometry results in more consistent readings, because each sensorplate 1305 will respond more uniformly to a change to surface or to theobject(s) being detected. The sensor plates 1305 that each respondsimilarly may be able to better detect obscured features that are deeperin a wall, or obscured features that may be harder to detect. Withsimilar electric fields the result may be an obscured feature detectorthat can be used on a variety of different surfaces and may performequally well on each of the variety of different surfaces. The resultmay also be an obscured feature detector that can sense more deeply, ormore accurately, or both.

In some embodiments an obscured feature detector may have a common platethat is less than the collective linear dimension of the three or moresensor plates. This configuration may result in forming electric fieldsthat have a similar size, shape, and/or geometry. In some embodiments anobscured feature detector may have a common plate that is less than thecollective linear dimension of the three or more sensor plates plus 16millimeters. This configuration of a common plate less than a length ofthe sensor array plus 16 millimeters may result in electric fields thathave a similar size, shape, direction, and/or geometry. In other words,in some embodiments there may be a length that is defined as anarray-plus length. This array-plus length may be at most 16 millimeterslonger than the collective length of the sensor array. In someembodiments this array-plus length may be at most one and a half times asensor width longer than the collective length of the sensor array. Inother words, the length of the common plate may measure longer than thearray by at most one and a half times a width of a sensor plate (e.g., awidth of an end sensor plate). An obscured feature detector that has acommon plate that is less than the array-plus length may be called ashortened common plate. In some embodiments an obscured feature detectorthat has a shortened common plate may have electric fields that eachhave a more similar size, shape, direction, and/or geometry.

A result of the increased similarity of the electric fields may be thatthe obscured feature detector can sense more accurately and more deeplyinto and/or through a surface.

An obscured feature detector with a shortened common plate may haveelectric fields that each have a more similar size, shape, direction,and/or geometry, as compared to obscured feature detectors with a commonplate described in the prior art. More uniformity in the size, shape,direction, or geometry of the electric fields associated with eachsensor plate may provide more uniform readings for each of the sensorplates. Sensor plates that each have similar electric fields may eachrespond in a more uniform manner to different surface materials andthicknesses. For example, one embodiment of an obscured feature detectorwith a shortened common plate may be placed on a particular surface,such as a surface of 0.25-inch-thick sheetrock. When placed on thissurface each of the sensor plates may each have the same reading, suchas a reading of 100 units, for example. In this example if the sameobscured feature detector is placed on a different surface, such as0.50-inch-thick sheetrock, each of the readings may change to adifferent value, but once again each of the sensor plate readings may besimilar, such as a value of 200 units. When the readings from each ofthe sensor plates provide similar readings, independent of whateversurface the obscured feature detector is placed upon, any variation insensor plate readings may be attributed to the presence of an obscuredfeature. Obscured feature detectors with shortened common plates maymaintain a greater uniformity in the readings, across differentsurfaces, than prior art obscured feature detectors. Readings that areuniform, independent of the surface, may make it possible to sense moreaccurately and more deeply, identify feature width more accurately, andmake it possible to sense two objects simultaneously more precisely. Insome embodiments a shortened common plate may have the advantageousresult of the sensing field for each sensor plate being positioned moreprecisely in the region near the sensor plate. As a result, the obscuredfeature detector may sense more accurately and more deeply.

In some presently available obscured feature detectors the common plateis less than 8.00 millimeters wide. In some embodiments of an improvedobscured feature detector there may be improved performance if thecommon plate is more than 8.00 millimeters wide. Obscured featuredetectors that have a common plate that is more than 8.00 millimeterswide may have electric fields that each have a more similar size, shape,direction, and/or geometry, as compared to obscured feature detectorswith a common plate described in the prior art.

As shown in FIG. 15, the obscured feature detector 1300 may have aprimary coupling area 1502 of the end sensor plate 1310 of the sensorarray 1307 on a first line 1520 with the corresponding primary couplingarea 1504 of the one or more common plates. The obscured featuredetector 1300 may also have a primary coupling area 1512 of the non-endsensor plate 1314 of the sensor array 1307 on a second line 1522 with acorresponding primary coupling area 1514 of the one or more commonplates. In some embodiments, the first line 1520 and the second line1522 are non-parallel. This may result in electric fields that have amore-similar size, shape, direction, and geometry.

In other words, if the origin and termination of the electric fieldcorresponding to the non-end sensor plate 1314 is on the first line1520, and if the origin and termination of the electric fieldcorresponding to the end sensor plate 1310 is on the second line 1522,and if the first line 1520 and the second line 1522 are non-parallel,then the electric fields 1506 corresponding to the end sensor plates1310 may be more similar to the electric fields 1508 corresponding tonon-end sensor plates 1314 than would be the case if the first andsecond lines 1520, 1522 were parallel. The result may be that each ofthe sensor plates 1305 may have a more uniform response to changes inthe surface or object being detected. As a result, the obscured featuredetector 1300 may sense more accurately and more deeply.

For example, if the presence of an obscured feature causes one of thesensor plates 1305 to have a particular reading when an object is placedin proximity to the sensor plate 1305, it would be desirable for each ofthe sensor plates 1305 to have the same reading when the obscuredfeature is placed in the same position relative to the sensor plate1305. The uniform response just described may make it possible to sensemore independently of the surface material or thickness. The result maybe that studs are sensed more accurately, independent of the surfacematerial or thickness.

The plate configuration of the embodiment of an obscured featuredetector 1300 of FIG. 15 causes the electric field 1506 formed from anend sensor plate 1310 and the electric field 1508 formed from a non-endsensor plate 1314 to have a similar size, shape, or orientation. This isin contrast with the electric fields shown in FIG. 14. The uniformity ofthe electric fields may increase the accuracy of an obscured featuredetector. The increased accuracy may be a result of the electric fieldsof each sensor plate 1305 taking a similar reading (e.g., a readingcovering a similar depth and width).

FIG. 16 illustrates the electric fields 1606, 1608 emitted from an endsensor plate 1310 and a non-end sensor plate 1314 for a plateconfiguration of an obscured feature detector 1600 with multiple commonplates 1601. As shown, the multiple common plates 1601 may be sized,configured, and aligned to cause the electric field 1606 formed from anend sensor plate 1310 to have a similar size, shape, and/or orientationto the electric field 1608 formed from a non-end sensor plate 1314. Themultiple common plates 1601 may be arranged linearly to extend along thelength of the sensor array 1307.

Just as in FIG. 15, a primary coupling area 1602 of the end sensor plate1310 of the sensor array 1307 is on a first line 1620 with acorresponding primary coupling area 1604 of the multiple common plates1601. Further, a primary coupling area 1612 of a non-end sensor plate1314 of the sensor array 1307 is on a second line 1622 with thecorresponding primary coupling area 1614 of the multiple common plates1601. Due to the positioning of the multiple common plates 1601, thefirst line 1620 and the second line 1622 are non-parallel causing theelectric field 1606 formed from the end sensor plate 1310 to have asimilar geometry to the electric field 1608 formed from the non-endsensor plate 1314. The uniformity of the electric fields 1606, 1608 mayincrease the accuracy of the obscured feature detector 1600. Each of themultiple common plates 1601 may be independently activated. In someembodiments the multiple common plates 1601 may be activated by beingcoupled to an unchanging voltage level, such as 0 volts, or 3 volts, orany other unchanging voltage level. In some embodiments the multiplecommon plates 1601 may be activated by being driven with an alternatingvoltage.

FIG. 17 is a flow chart illustrating a method 1700 of detecting anobscured feature behind a surface. The method may include taking 1702 asensor reading between the three or more sensor plates and a shortenedcommon plate of an obscured feature detector. The three or more sensorplates may be arranged linearly in a sensor array. The sensor readingmay be of a region of a sensing field formed between the three or moresensor plates and a common plate of the obscured feature detector. Thecommon plate may be less than a dimension of the sensor array.

The method may further include measuring 1704, via a sensing circuit,the sensor readings of the three or more sensor plates, and comparing1706 measurements of sensor readings in different regions of the sensingfield. The measured sensor reading may be a capacitive reading or anelectromagnetic reading. Further, the method may toggle 1708 indicatorsfrom a deactivated state to an activated state to indicate a location ofa region of the sensing field having a relatively high sensor reading.

FIG. 18 illustrates an obscured feature detector 1800, according toanother embodiment of the present disclosure, with an alternativeconfiguration of a plurality of sensor plates 1805. The obscured featuredetector 1800 includes an end sensor plate 1874 of a sensor array 1807that has less area than the non-end sensor plates. In this embodimentthe end sensor plate 1874 is narrower than the non-end sensor plate 1875of the sensor array 1807. Each sensor plate 1805 in the sensor array1807 is configured to be electrically coupled to a common plate 1876 viaan electric field 1881, 1882. Each sensor plate 1805 in the sensor array1807 is configured to provide a primary coupling area 1879, 1880 thatmay form a first end of the electric field 1881, 1882. Further, thecommon plate 1876 is configured to provide a corresponding primarycoupling area 1885, 1886 to correspond to each of the end sensor plates1874 and the non-end sensor plates 1875 and form a second end of thecorresponding electric field 1881, 1882 of each sensor plate 1805.

The primary coupling area 1879 of the end sensor plate 1874 is on afirst line 1883 that extends from the primary coupling area 1879 of theend sensor plate 1874 to the primary coupling area 1885 of the commonplate 1876. The primary coupling area 1880 of a non-end sensor plate1875 is on a second line 1884 that reaches from the primary couplingarea 1880 of the non-end sensor plate 1875 to the primary coupling area1886 of the common plate 1876.

In the configuration of FIG. 18, the common plate 1876 has a length 1878that is greater than the length 1888 of the sensor array 1807. In someembodiments the length 1878 of the common plate 1876 may be equal (orclosely similar) to the length of the shielding plate 1877 locatedbetween the common plate 1876 and the sensor array 1807. The non-endsensor plates 1875 each have a length 1873 and width 1871 that areidentical (or closely similar) to the length and width of the othernon-end sensor plates 1875 in the sensor array 1807. The end sensorplates 1874 have lengths 1872 that are equal (or closely similar) to thelengths 1873 of the non-end sensor plates 1875, but widths 1870 that aresmaller than the widths 1871 of the non-end sensor plates 1875.

As can be appreciated, the total area of the end sensor plate 1874 isless than that of a non-end sensor plate 1875. The smaller sensor areamay make the end sensor plates less responsive to changes in the surface2, such that the responsiveness of the end sensor plates more closelymatches the responsiveness of the non-end sensor plates. In some priorart obscured feature detectors the end sensor plates and the non-endsensor plates each have different responses to changing surfaces 2, orto changing obscured features 3. This is responsiveness issue isdiscussed in the dialog surrounding FIG. 7 and FIG. 8. The end sensorplate 1879 may have less area may be less responsive to differentsurfaces and to different obscured features, as a result it may have aresponse that is more similar to the non-end sensor plates 1875.Further, the electric field 1881 formed between an end sensor plate 1874and the common plate 1876 will be smaller than were the width 1870 ofthe end sensor plate 1874 identical (or closely similar) to the width1871 of the non-end sensor plates 1875. In other words, the narrowerwidth 1870 of the end sensor plate 1874 results in a smaller electricfield 1881 that is more similar in shape (including more similar indepth into the surface of detection) to the electric field 1882 betweena non-end sensor plate 1875 and the common plate 1876. In contrast tothe electric field 1406 in FIG. 14 that couples a wide end sensor plate1210 to the common plate 1202, the electric field 1881 in FIG. 18between the coupling areas 1879, 1880 of a narrow end sensor plate 1874and the common plate 1876 does not diverge as drastically as an endsensor plate having the same width as a non-end sensor plate 1875. Theelectric fields 1881 between the end sensor plates 1874 and the commonplate 1876 are more similar to the electric fields between non-endsensor plates 1875 and the common plate 1876. As noted previously, themore similar shape of the electric field 1881, 1882 translates in morepredictable readings of the sensor plates, and thereby more accuratedetections of obscured features.

In various embodiments according to the configuration illustrated byFIG. 18, if the electric fields 1881, 1882 are relatively similar insize, shape, direction, and/or geometry between sensor plates 1874, 1875in a sensor array 1807, the sensor plates 1874, 1875 may each respondsimilarly to an obstruction in the path of their electric fields 1881,1882. Stated another way, greater uniformity of the end electric fields1881 with the non-end electric fields 1882 enables more consistentreadings, because each of the sensor plates 1805 will respond moreuniformly to a change to a surface or to the object(s) being detected.Sensor plates 1805 that each respond similarly may be able to betterdetect obscured features that are deeper in a wall, or obscured featuresthat may be harder to detect. With similar electric fields 1881, 1882,an obscured feature detector may result that can be used on a variety ofdifferent surfaces and may perform equally well on each of the varietyof different surfaces. The obscured feature detector 1800 with uniformend electric fields 1881 and non-end electric fields 1882 can sense moredeeply, or more accurately, or both.

FIG. 19 illustrates an obscured feature detector 1900, according toanother embodiment of the present disclosure, that is similar to FIG. 18and with an alternative end sensor plate configuration. The end sensorplates 1981 have a different shape than the other sensor plates. In theobscured feature detector 1900 of FIG. 19, the end sensor plates 1981have a trapezoidal shape. In some embodiments, the end sensor plates1981 of a shape different than other sensor plates may enable the endsensor plates 1981 to detect obscured features more similarly to non-endsensor plates.

The end sensor plates 1981 may have the same length 1985 as the non-endsensor plates 1982, but the lower width 1984 is wider than the upperwidth 1988. In some embodiments, the lower width 1984 of the end sensorplates 1981 may be equal to the lower width 1986 of the non-end sensorplates 1982, and the upper width 1988 of the end sensor plates 1981 maybe smaller. In some embodiments, the lower width 1984 of the end sensorplates 1981 may be greater than the width 1986 of the non-end sensorplates 1982, and the upper width 1988 of the end sensor plates 1981 maybe equal to the width 1986 of the non-end sensor plates 1982. In someembodiments both the upper 1988 and lower widths 1984 may be greaterthan the width 1986 of the non-end sensor plates 1982, and the lowerwidth 1984 of the end sensor plates 1981 is greater than the upper width1988 of the end sensor plates 1981. In some embodiments both the upper1988 and lower widths 1984 may be smaller than the width 1986 of thenon-end sensor plates 1982, and the lower width 1984 of the end sensorplates 1981 is greater than the upper width 1988 of the end sensorplates 1981.

FIG. 20 illustrates an obscured feature detector 2001, according to oneembodiment, placed on a piece of sheetrock 2002 (or similar surface) anddetecting an obscured feature 2003. FIG. 21 is a perspective view of theobscured feature detector 2001 of FIG. 20. FIG. 22 shows a sensor sideof the obscured feature detector 2001, which includes a plurality ofsensor plates 2205.

With reference to FIGS. 20-22, generally and collectively, the obscuredfeature detector 2001 includes three or more sensor plates 2205, asensing circuit (see FIG. 23), one or more indicators 2006, one or moreproximity indicators 2039, and a housing 2019 to provide or otherwiseaccommodate a handle 2014, an active shield plate 2623 (see FIG. 26),and a battery cover 2028.

The three or more sensor plates 2205 each can take a sensor reading thatvaries based on a proximity of the sensor plate 2205 to one or moresurrounding objects and on a material property of each of the one ormore surrounding objects. The three or more sensor plates 2205collectively create a sensing field. Each individual sensor plate 2205of the three or more sensor plates 2205 creates a corresponding primarysensing field zone that may be a geometric three-dimensional volumewithin the sensing field where the individual sensor plate 2205contributes more strongly to the sensing field than any other of thethree or more sensor plates 2205. The three or more sensor plates 2205all create primary sensing field zones that are geometrically similar.The sensing circuit couples to the three or more sensor plates 2205 tomeasure the sensor readings of the three or more sensor plates 2205.

In some embodiments each sensor plate 2205 may be part of a group 2207of sensor plates 2205. Each group 2207 may include two or more sensorplates 2205 and may also include an active shield plate 2623. The sensorplates 2205 and active shield plate 2623 may be on different planes.Nevertheless, if they are driven simultaneously, in some embodiments,they may be part of the same group 2207 of sensor plates 2205. Eachsensor plate 2205 has a geometry that is defined by its shape. Eachsensor plate 2205 also has a perimeter. In some embodiments theperimeter may be composed of multiple segments. In some embodiments eachsegment of the perimeter is either an internal border 2210 or anexternal border 2211. In some embodiments, if a sensor plate 2205 has asegment of the perimeter that is adjacent to the perimeter of the group2207, then said segment comprises an external border 2211. In someembodiments, if a sensor plate 2205 has a segment of the perimeter thatis not adjacent to the perimeter of the group 2207, then said segmentcomprises an internal border 2210.

In some embodiments to sense the location of an obscured feature 2003, asensor plate 2205 may be driven with a current source, and the obscuredfeature detector 2001 measures the time it takes for the sensor plate2205 to reach a certain threshold voltage, thereby achieving a sensorreading. In other embodiments a charge-share mechanism is used toachieve a sensor reading. In other embodiments a radio frequency signalis placed on the sensor plates 2205 to achieve a sensor reading. In eachof these embodiments a signal is driven on the sensor plate(s) 2205 tobe sensed.

In some embodiments, only a single sensor plate 2205 may be driven at atime. In these embodiments the single sensor plate 2205 may be alone increating the sensing field.

In some embodiments, a group 2207 of sensor plates 2205 may all bedriven with the same signal simultaneously. In these embodiments thegroup 2207 of sensor plates 2205 may create the sensing field. In someembodiments multiple sensor plates 2205 may be driven simultaneouslyeach with the same signal, although possibly only a single sensor plate2205 may be sensed. Advantageously driving multiple sensor plates 2205simultaneously may create field lines that go deeper into an obscuredsurface than may be possible if only a single sensor plate 2205 isdriven. Deeper field lines may make it possible to sense more deeply. Insome embodiments a group 2207 of sensor plates 2205 and an active shieldplate 2623 may all be driven with the same signal simultaneously, whichtogether would create the sensing field.

Each sensor plate 2205 has a primary sensing field zone. In someembodiments the primary sensing field zone is a geometricthree-dimensional volume of the sensing field and associated field lineswhere the individual sensor plate 2205 is able to sense more stronglythan the active shield plate 2623 (if present) or any other sensor plate2205. In some embodiments it is desirable for each sensor plate 2205 tohave similar primary sensing field zones. In some embodiments it isdesirable for each sensor plate 2205 to have primary sensing field zonesthat are geometrically similar and to have similar sensing fields withintheir respective primary sensing field zones.

FIG. 22 illustrates a group 2207 of eight sensor plates 2205. Each ofthe eight sensor plates 2205 is triangular. Each triangular sensor plate2205 has two segments that each have internal borders 2210. Each sensorplate 2205 also has one segment that has an external border 2211.

In some embodiments, as shown in FIG. 22, the group 2207 may compriseeight triangular sensor plates 2205 that each have a similar geometry.The group 2207 of sensor plates 2205 may be arranged within a squarearea, wherein each side of the square area is approximately 3 incheslong. In some embodiments, each of the sensor plates 2205 may be in theshape of an isosceles triangle. In some embodiments the sensor plates2205 may be arranged such that the hypotenuse of two triangular sensorplates 2205 may be adjacent to each other, as shown in FIG. 22. In someembodiments two sensor plates 2205 with adjacent hypotenuses mayapproximate a square and fit within one quadrant of the group 2207 ofsensor plates 2205. In some embodiments there may be two such trianglespositioned in each quadrant such that the entire group 2207 compriseseight sensor plates 2205, as shown in FIG. 22. In some embodiments thedistance between adjacent sensor plates 2205 may be approximately 2.0mm.

In FIG. 22 a sensing field may be created collectively by the eightsensor plates 2205. In some embodiments an active shield plate 2623 maycontribute to the sensing field. In the embodiment of FIG. 22 each ofthe sensor plates 2205 may have similar primary sensing field zones. Inthis embodiment, the radial symmetry of the sensor plates 2205 mayprovide each sensor plate 2205 with primary sensing zones that aregeometrically similar. Likewise, each of the sensor plates 2205 may alsohave similar sensing fields within their respective primary sensingfield zones. As a result, an obscured feature detector 2001 that isbuilt with a configuration of FIG. 22 may offer improved performance.When the obscured feature detector 2001 is moved from a thin surface toa thicker surface the sensor readings for each of the sensor plates 2205may have a similar increase in value.

In some embodiments a sawtooth-shape border or perimeter may have thesame effective border as a straight-line border that does not have asawtooth. In some embodiments a border with a very slight curve may havethe same effective border as a straight-line border that does not have aslight curve. In some embodiments a sensor plate 2205 with a slot in ithas the same effective geometry as an otherwise equivalent sensor plate2205 without a slot. In some embodiments a sensor plate 2205 with asmall hole in it may have the same effective geometry as an equivalentsensor plate 2205 without a hole. Many other geometries are possiblethat may be effectively equivalent to other substantially equivalentgeometries. Many other borders are possible that may effectively beequivalent to other substantially equivalent borders. If a geometry or aborder has a property that is effectively equivalent to another geometryor border, then the two may be considered to be similar.

In some embodiments a group 2207 of sensor plates 2205 is configuredsuch that each sensor plate 2205 in the group 2207 has the samegeometry. In some embodiments each of the sensor plates 2205 in thegroup 2207 is radially symmetrical.

The plurality of indicators 2006 may be toggled between a deactivatedstate and an activated state to indicate a location within the sensingfield of a region of relative high sensor reading. Activated indicators2004 can indicate the position of the obscured feature 2003. Proximityindicators 2039 can indicate that the obscured feature detector 2001 maybe near the obscured feature 2003.

In FIGS. 20-22, the indicators 2006 are positioned on a layer above thesensor plates 2205. In some embodiments there may be an active shieldplate 2623 between the sensor plates 2205 and the indicators 2006 sothat the indicators 2006 do not interfere with the function of thesensor plates 2205. In some embodiments it may be desirable to positionthe indicators 2006 on a layer above the sensor plates 2205 so that eachof the sensor plates 2205 may have a similar distance from the sensorplate 2205 to the edge of a corresponding PCB.

In some embodiments, a layer of protective material is mounted to thebottom of the obscured feature detector 2001, such that there is a layerof protective material between the surface 2002 and the obscured featuredetector 2001. In some embodiments, the protective material has theinterior substantially filled such that it is substantially free fromcavities. In some embodiments the protective material is unlike felt,Velcro, cloth, or other materials that have an interior with cavities.The layer of protective material may serve the purpose of protecting thebottom of the obscured feature detector 2001 from damage due to knocks,bumps, and wear-and-tear. The protective material could be made from asolid piece of material, such as plastic or other solid non-conductivematerials. A solid layer of plastic may provide a low friction surfacethat would allow the obscured feature detector 2001 to slide across thewall. Although some embodiments of the obscured feature detector 2001 donot require sliding to operate, a low friction surface may be useful tosome users who may choose to move the obscured feature detector 2001from position to position by sliding it.

The protective layer of plastic may be mounted with a pressure sensitiveadhesive, glue, or other means. The layer of protective material may bea complete layer that covers the entire surface; it may be rectangularstrips, round pieces, or other layers of plastic with other geometries.

A protective material that is substantially filled such that it issubstantially free from cavities may build up less static charge thanprior art solutions and may advantageously provide for more consistentsensor readings.

In some embodiments the protective material is UHMW-PE (Ultra-HighMolecular Weight Polyethylene). UHMW-PE has a low coefficient offriction. UHMW-PE also absorbs very little moisture which may provideincreased immunity from changes in humidity, and may provide enhancedimmunity from changes in humidity.

FIG. 23 is a diagram of a circuit of an obscured feature detector 2301,according to one embodiment. The circuit includes a multiplexer 2318, apower controller 2320, a display circuit 2325, a sensing circuit 2327,and a controller 2360.

The power controller 2320 may include a power source 2322 and an on-offbutton 2324. The power source 2322 can comprise an energy source forpowering the indicators 2306 and supplying power to acapacitance-to-digital converter 2321, and the controller 2360. In someembodiments, the power source 2322 can comprise a DC battery supply. Theon-off switch 2324 can be used to activate the controller 2360 and othercomponents of the obscured feature detector 2001. In some embodiments,the on-off switch 2324 comprises a push-button mechanism that activatescomponents of the obscured feature detector 2001 for a selected timeperiod. In some embodiments the push button activates the componentssuch that the components remain activated until the button is released.In some embodiments the on-off switch 2324 comprises a capacitive sensorthat can sense the presence of a finger or thumb over the button. Insome embodiments, the on-off switch 2324 can comprise a toggle switch orother types of buttons or switches.

The display circuit 2325 may include one or more indicators 2306 thatare electronically coupled to the controller 2360.

The sensing circuit 2327 may include a voltage regulator 2326 and thecapacitance-to-digital converter 2321. In some embodiments, as shown inFIG. 23, the sensing circuit 2327 comprises a plurality of sensors, thevoltage regulator 2326, and the capacitance-to-digital converter 2321.The voltage regulator 2326 may be used to condition the output of thepower controller 2320, as desired. In some embodiments the voltageregulator 2326 is placed as near as possible to thecapacitance-to-digital converter 2321, which may provide a better powersource 2322 to the capacitance-to-digital converter 2321. The sensingcircuit 2327 can be electrically coupled to the controller 2360. One ormore sensor plate traces 2335, or electrically conductive paths on thePCB, may connect the individual sensor plates 2305 to thecapacitance-to-digital converter 2321. The connection of the sensorplates 2305 to the capacitance-to-digital converter 2321 may be made viathe multiplexer 2318. The multiplexer 2318 can individually connect thesensor plates 2305 to the capacitance-to-digital converter 2321.

In some embodiments the multiplexer 2318 may connect a single sensorplate 2305 to the sensing circuit 2327. In some embodiments, themultiplexer 2318 may connect more than one adjacent sensor plate 2305 tothe sensing circuit 2327. In some embodiments, the multiplexer 2318 mayconnect more than one non-adjacent sensor plate 2305 to the sensingcircuit 2327. In some embodiments, the multiplexer 2318 is configured sothat the sensing circuit 2327 measures the capacitance of one sensorplate 2305. In some embodiments, the multiplexer 2318 is configured sothat the sensing circuit 2327 measures the aggregate capacitance of twoor more sensor plates 2305.

Each individual sensor plate 2305 of a group 2307 can be independentlyconnected to the capacitance-to-digital converter 2321 via themultiplexer 2318. In some embodiments, the group 2307 itself compriseslayers of copper on a PCB.

In some embodiments a two-layer PCB is configured as a sensor plateboard 2740 (see FIGS. 27 and 37). In some embodiments a first layer ofthe sensor plate board 2740 comprises the sensor plates 2305, and asecond layer of the sensor plate board 2740 comprises a shield. In someembodiments, the shield comprises a layer of copper that covers theentire surface of the second layer of the PCB. In some embodiments thelayer of copper is covered with a non-conductive layer of soldermask. Insome embodiments there are holes in the layer of soldermask. In someembodiments, the holes in the layer of soldermask comprise solder padsthat are suitable for making solder bonds.

In some embodiments a four-layer PCB is configured as an interconnectionboard that has interconnections suitable for connecting circuitrycomponents. In some embodiments the interconnection board is configuredwith four layers of interconnections that are suitable forinterconnecting the sensing circuit 2327, the controller 2360, and thedisplay circuit 2325. In some embodiments one side of the PCB isconfigured for mounting components, and a second side of the PCB isconfigured with solder pads.

In some embodiments the sensor plates 2305 are arranged on a first PCB.In some embodiments the interconnection circuitry is arranged on asecond PCB. In some embodiments the first PCB is bonded to the secondPCB.

In some embodiments there are solder pads on the sensor plate board 2740that are complementary with solder pads on an interconnection board. Insome embodiments the sensor plate board 2740 and the interconnectionboard 3751 may be stacked on top of one another and bonded to each other(e.g., FIG. 37). In some embodiments the bonding agent that bonds thetwo PCBs together may be solder. In some embodiments solder paste may beused to bond two PCBs together. In some embodiments, they may be bondedtogether with solder and the process to bond them together may bestandard SMT processes. The standard SMT process may include using astencil to place solder paste in the desired locations. The SMT processmay include placing one PCB on top of another. In some embodiments pinsmay be used to ensure proper alignment of the two PCBs. In someembodiments the final step of the SMT process may involve running thestacked PCBs through a reflow oven (e.g., FIG. 37 illustrates aninterconnection board 3751 stacked on top of a sensor plate board 2740).

In some embodiments the sensor plates 2305, shield, and circuitry areplaced on a single PCB. In some embodiments a six-layer PCB is used. Insome embodiments the bottom layer, which is the sixth layer, of the PCBis configured with sensor plates 2305. The fifth layer may be an activeshield. The top four layers may connect the balance of the circuitry.

In some embodiments the sensor plates 2305, shield, and circuitry areplaced on a single PCB. In some embodiments a four-layer PCB is used.First and second layers of the PCB are configured with interconnectioncircuitry. In some embodiments the bottom layer, which is the fourthlayer, of the PCB is configured with sensor plates 2305. The third layermay be an active shield.

The PCB can be made from a variety of suitable materials, such as, forexample, FR-4, FR-406, or more advanced materials used in radiofrequency circuits, such as Rogers 4003C. Rogers 4003C, and otherradio-frequency-class PCB substrates, may offer improved performanceacross a broader temperature and humidity range.

As used herein, the term “module” can describe any given unit offunctionality that can perform in accordance with one or moreembodiments of the present invention. For example, a module might byimplemented using any form of hardware or software, or a combinationthereof, such as, for example, one or more processors, controllers 2360,ASICs, PLAs, logical components, software routines, or other mechanisms.

Different processes of reading a capacitance and converting it to adigital value, also known as a capacitance-to-digital conversion, arewell-described in the prior art. The many different methods are notdescribed here, and the reader is referred to the prior art for detailsabout different capacitance-to-digital converter methods. Someembodiments use a sigma-delta capacitance-to-digital converter, such asthe one that is built into the Analog Devices AD7747 integrated circuit.Some embodiments use a charge-sharing method of capacitance-to-digitalconversion.

In some embodiments the voltage regulator 2326 may comprise theADP150-2.65 from Analog Devices, or the NCP702 from ON Semiconductor,which provide very low noise. In some embodiments, the controller 2360may comprise the C8051F317 from Silicon Laboratories, or any of manyother microcontrollers.

Detecting obscured features 2003 can require a high degree of accuracy,and may require more accuracy than the capacitance-to-digital converter2321 may be able to provide, if the native capacitance-to-digitalconverter 2321 sensor readings are used alone. Native sensor readingsare the raw values read from the capacitance-to-digital converter 2321;they are the digital output of the capacitance-to-digital converter2321.

Some embodiments perform native reads multiple times, and combine theresults of the multiple native reads, to create a reading. Someembodiments perform native reads multiple times, and combine the resultsof the multiple native reads, using a different configuration for two ormore of the native reads to create a reading. Some embodiments performnative reads multiple times, and sum or average the results of themultiple native reads, to create a reading. In some embodiments thisimproves the signal-to-noise ratio. Each native read may involve readingone sensor plate 2305. A native read could also involve reading aplurality of sensor plates 2305, if multiple sensor plates 2305 aremultiplexed to the capacitance-to-digital converter 2321. In someembodiments multiple native reads are combined to create a reading.

Summing or averaging multiple native reads may improve thesignal-to-noise ratio, but may not reduce the effect of non-linearitiesin the capacitance-to-digital converter 2321. The idealcapacitance-to-digital converter 2321 is perfectly linear, which meansthat its native sensor readings increase in direct proportion to anincrease in the capacitance being sensed. However, manycapacitance-to-digital converters 2321 may not be completely linear,such that a change in the input capacitance does not result in anexactly proportional increase in the native reading. Thesenon-linearities may be small, but when a high degree of accuracy isdesired it may be desirable to implement methods that reduce the effectsof the non-linearities.

In some embodiments, the ill effects of the non-linearities may bemitigated by summing multiple native reads, using a slightly differentconfiguration for each of the native reads. Some embodiments performnative reads using two or more different configurations.

For example, the bias current is one parameter that can be altered tocreate different configurations. The bias current could be set tonormal, or normal +20%, normal +35%, or normal +50%. Different biascurrents produce different native sensor readings, even if all otherfactors remain constant. Since each native reading has a differentvalue, presumably each native reading may be subject to differentnon-linearities. Presumably summing or averaging sensor readings thatare subject to different non-linearities may cause the non-linearitiesto partially cancel each other out, instead of being summed ormultiplied.

In some embodiments there are two separate and independentcapacitance-to-digital converters 2321. In some embodiments each of themmay have different non-linearities. Using both of thecapacitance-to-digital converters 2321, using the first converter forsome of the reads and using the second converter for some of the reads,may mitigate the effect of any single non-linearity.

Some embodiments perform native reads on each of the sensor plates 2305using each of twelve different configurations.

After completing the sensor readings, in some embodiments, two differentcalibration algorithms may be performed: first an individual-platecalibration that adjusts for individual sensor plate 2305 variations,and second a surface material calibration that adjusts the sensorreadings so that they are tuned to the surface density/thickness. Otherembodiments may only use one of the two calibration algorithms. Someembodiments may use other calibration algorithms. In some embodimentsthe calibration algorithms are performed by a calibration module.

In some embodiments, individual plate calibration is employed first.With individual plate calibration, each sensor plate 2305 may have itsown individual calibration value. In some embodiments, after the sensorreadings are taken, an individual plate calibration value is added to,or subtracted from, each of the sensor readings. Other embodiments mayuse multiplication, division, or other mathematical functions to performthe individual plate calibration. In some embodiments, the individualplate calibration value is stored in non-volatile memory. Individualplate calibration compensates for individual sensor plate 2305irregularities, and is used to compensate for these irregularities. Insome embodiments it is presumed that after performing individual platecalibration that the sensor readings will presumably have the samecalibrated values, if the sensor plate sensor readings are taken whilethe obscured feature detector 2301 is on a surface that is similar tothe surface 2002 the obscured feature detector 2001 was calibrated on(see e.g., FIG. 22). For example, if sensor readings are performed on ½″sheetrock 2002, without any obscured features 2003 present, and theindividual calibration values were created for ½″ sheetrock 2002, thenafter performing individual plate calibration, it is presumed that allthe sensor readings would be corrected to a common value. If sensorreadings are performed on a thicker material (such as ⅝″ sheetrock2002), a thinner material (such as ⅜″ sheetrock 2002), or a differentmaterial (such as ¾″ plywood) then there may be some error in thevalues. Surface material calibration may help correct this error.

In some embodiments surface material calibration may be used.

In some embodiments, after calibrating the sensor plate sensor readingsthe obscured feature detector 2301 decides if an obscured feature 2003is present. In some embodiments the lowest sensor plate reading issubtracted from the highest sensor plate reading. If the difference isgreater than a threshold value then a determination is made that anobscured feature 2003 is present.

If it is determined that no obscured features 2003 are present, then allof the indicators 2306 may be deactivated. If an obscured feature 2003is present then the obscured feature detector 2301 begins the process ofdetermining the position(s) and width(s) of the obscured feature(s)2003.

In some embodiments pattern matching may be employed to determine whichLEDs to activate. In some embodiments a pattern matching module is usedto determine the locations of the obscured features 2003. The patternmatching module compares the calibrated and scaled sensor readings fromthe sensor plates 2305 to several predetermined patterns. The patternmatching module determines which predetermined pattern best matches thesensor readings. Then the set of indicators 2306 that corresponds to thebest matching pattern is activated. Additional details about patternmatching are discussed in the prior art, such as in U.S. Pat. No.8,884,633. Those details will not be repeated here; instead the readeris encouraged to refer to them directly.

In some embodiments the obscured feature detector 2301 comprises asingle capacitance-to-digital converter 2321. In some embodiments thesensor plates 2305 may be individually connected to thecapacitance-to-digital converter 2321. In some embodiments the sensorplates 2305 may be individually connected to the capacitance-to-digitalconverter 2321 via the multiplexer 2318. In some embodiments more thanone sensor plate 2305 may be connected to the capacitance-to-digitalconverter 2321 at a time. In some embodiments multiple adjacent sensorplates 2305 may be electrically connected to the capacitance-to-digitalconverter 2321. In some embodiments multiple non-adjacent sensor plates2305 may be connected to the capacitance-to-digital converter 2321. Theuse of the multiplexer 2318 to connect sensor plates 2305 to a singlecapacitance-to-digital converter 2321 may improve sensor plate 2305 tosensor plate 2305 consistency of the sensor readings, because the sensorreadings from each of the sensor plates 2305 may be equally affected byvariations to the capacitance-to-digital converter 2321. Factors thatmay affect the sensor readings from the capacitance-to-digital converter2321 may include, but are not limited to, process variations,temperature variations, voltage variations, electrical noise, aging, andothers.

In some embodiments, the sensor plate traces 2335 are routed such thateach of the sensor plate traces 2335 has substantially equalcapacitance, resistance, and inductance. In some embodiments it isdesirable for each of the sensor plate traces 2335 to have the sameelectrical properties, so that each of the sensor plates 2305 willrespond equivalently to the same detected object(s).

In some embodiments each of the sensor plate traces 2335 from thecapacitance-to-digital converter 2321 to each of the sensor plates 2305has substantially the same length (see, e.g., FIG. 25). In someembodiments two or more of the sensor plate traces 2335 from thecapacitance-to-digital converter 2321 to the sensor plates 2305 havesubstantially the same length. In some embodiments sensor plate traces2335 with substantially the same length may have more equivalentcapacitances, inductances, and resistances. Equal length sensor platetraces 2335 may offer enhanced performance because they may improve theuniformity of the sensor readings, such that the sensor plates 2305respond more equivalently to the same detected objects, and may providemore immunity from environmental conditions, such as temperature andhumidity.

In some embodiments each of the sensor plate traces 2335, whichcomprises electrically conductive paths, has substantially the samewidth. In some embodiments, both the width and the length of each of thesensor plate traces 2335 are substantially equivalent. In someembodiments the sensor plate traces 2335 will have more than onesegment. For example, a first segment of the traces may route the sensorplate traces 2335 from a capacitance-to-digital converter 2321 to a via.The via may take the sensor plate trace 2335 to a different layer of thePCB, where there may be a second segment of the sensor plate trace 2335.In some embodiments all of the sensor plate traces 2335 will have thesame length and width, in each segment, as the other traces in thatsegment. In some embodiments two or more of the sensor plate traces 2335will have the same width throughout a first segment. In some embodimentstwo or more of the sensor plate traces 2335 will have the same widththroughout a second segment. In some embodiments two or more of thesensor plate traces 2335 will have the same length throughout a firstsegment. In some embodiments two or more of the sensor plate traces 2335will have the same length throughout a second segment.

In some embodiments the sensor plate traces 2335 comprise multiplesegments. In some embodiments a segment of a sensor plate trace 2335 maybe the wire bonds that are within the package of an integrated circuitthat route the signals from the piece of silicon to the pins of theintegrated circuit package. In some embodiments a segment of a sensorplate trace 2335 may comprise a layer of copper on a first layer of aPCB. In some embodiments a segment of a sensor plate trace 2335 maycomprise a layer of copper on a second layer of a PCB.

In some embodiments the capacitance-to-digital converter 2321 will readthe sum of the capacitance on the sensor plates 2305 and the capacitanceon the sensor plate traces 2335. In some embodiments, only detecting thesensor readings on the sensor plates 2305, and not detecting the sensorplate traces 2335, may be preferable. However, because the sensor plates2305 and sensor plate traces 2335 are electrically coupled, a means ofensuring stable and uniform capacitance on the sensor plate traces 2335may be desired. For example, it may be desirable to configure the sensorplate traces 2335 so that their capacitance is uniform and stable.Consequently, it may be preferred for the sensor plate traces 2335 to beconfigured so that the sensor plate traces 2335 do not change. In someembodiments it may be preferred that the sensor plate traces 2335 do notchange relative to each other, such that any change in the capacitanceon one sensor plate trace 2335 is reflected in each of the sensor platetraces 2335.

In some embodiments it may be advantageous to shield the sensor platetraces 2335. Sensor plate trace shielding may protect the sensor platetraces 2335 from external electromagnetic fields. In some embodimentsshielding the sensor plate traces 2335 may also advantageously provide amore consistent environment for the sensor plate traces 2335 by helpingto ensure that each of the sensor plate traces 2335 has an environmentthat is similar to each of the other sensor plate traces 2335.

In some embodiments each of the sensor plate traces 2335 from thecapacitance-to-digital converter 2321 to each of the sensor plates 2305has substantially the same surroundings. In some embodiments the sensorplate traces 2335 are routed sufficiently far apart so that capacitiveand inductive coupling between the sensor plate traces 2335 isminimized, and may improve consistency because each of the sensor platetraces 2335 may have surroundings that are more similar to the othersensor plate traces 2335. In some embodiments each of the sensor platetraces 2335 is shielded on one or both sides with an active shield trace(see, e.g., FIG. 25).

In some embodiments a user 2329 may be electrically coupled to thesensing circuit 2327. In some embodiments the quality of the sensorreadings is increased when an electrically conductive point of thesensing circuit 2327 is coupled to the user 2329. Electrically couplingthe user 2329 to the sensing circuit 2327 may provide a stationaryvoltage level for the sensing circuit 2327 and may result in higherquality sensor readings that have higher sensitivity. For example, aprior art obscured feature detector that drives the sensor plates 2305with a 3.0V may in reality only drive the sensor plates 2305 with a 3.0Vsignal relative to ground. However, if the ground is floating, thendriving the sensor plates 2305 with 3.0V could result in a 1.5V signalon the sensor plates 2305 and a −1.5V signal on the ground.

In some embodiments electrically coupling the user 2329 to the sensingcircuit 2327 may result in higher absolute voltage swings on the sensorplates 2305, which may be due in part to the sensing circuit 2327 beingheld at a stable level. In some embodiments electrically coupling theuser 2329 to the sensing circuit 2327 may also result in sensor readingsthat are more consistent.

In some embodiments the user 2329 is electrically coupled to the groundof the sensing circuit 2327, as shown in FIG. 23. In some embodimentsthe user 2329 is electrically coupled to the voltage source of thesensing circuit 2327. In some embodiments the user 2329 is electricallycoupled to a different electrically conductive point of sensing circuit2327.

In some embodiments the hand of the user 2329 may be electricallycoupled to the sensing circuit 2327 by making direct contact with thesensing circuit 2327. In some embodiments an electrically conductivematerial, such as a wire, may electrically couple the hand of the user2329 to the sensing circuit 2327. In some embodiments the button, whichthe user 2329 would need to touch to activate the obscured featuredetector 2301, may comprise an electrically conductive material whichmay be electrically coupled to the sensing circuit 2327. In someembodiments the button may comprise aluminum or another electricallyconductive material such as tin-plated steel. In some embodiments analuminum button may be anodized, which may provide pleasing cosmetics.

In some embodiments the housing 2019 (see FIG. 21) of the obscuredfeature detector 2301 may comprise an electrically conductive material,such as an electrically conductive plastic. In some embodiments only aportion of the housing 2019 may comprise electrically conductiveplastic. The electrically conductive housing, or a portion of theelectrically conductive housing, may be coupled to an electricallyconductive point in the sensing circuit 2327, thereby coupling the user2329 to the sensing circuit 2327.

In some embodiments mixing carbon black with the plastic resin mayprovide electrically conductive properties. Many thermoplastics,including polypropylene and polyethylene, become electrically conductivewhen a carbon black is mixed into the plastic resin. In some embodimentsthe conductivity increases as the concentration of carbon black isincreased, advantageously making it possible to control the conductivityof the plastic. In some embodiments a plastic with a conductivity thatis less than about 25,000 ohms-cm provides sufficiently highconductivity to effectively couple the user 2329 to the sensing circuit2327. In some embodiments a higher degree of conductivity may bedesired. In some embodiments a lower degree of conductivity may bedesired. In some embodiments it is advantageous for the user 2329 to becoupled to the sensing circuit by a path with less than about 50mega-ohms.

In some prior art obscured feature detectors, a change in the positionof the hand of the user 2329 can cause a change in the sensor readings.This may occur in some prior art obscured feature detectors because thehand may form a portion of the path between the sensor plates 2305 andground. As a result, a change in hand position can cause a change in thesensor readings of the sensor plates 2305. Disadvantageously, this mayreduce the accuracy of the sensor readings.

If it were possible for the size and position of the hand of the user2329 to be constant, it may be possible to do a calibration adjustmentto mathematically remove the effect of the hand of the user 2329 fromthe raw sensor readings. However, in practice this may not be feasible.In practice the size, shape, and position of hands of different users2329 may vary too much to make a calibration adjustment practicallypossible.

To improve performance in light of the aforementioned issues, in someembodiments a conductive hand guard may be positioned between the handof the user 2329 and the sensor plates 2305. In some embodiments thehand guard may be grounded to the sensing circuit 2327, as illustratedin FIG. 23.

FIG. 24 is a diagram of the controller 2360, according to oneembodiment. The controller 2360 includes a processor 2461, a clock 2462,random access memory (RAM) 2464, a non-volatile memory 2465, and/oranother computer-readable medium. The non-volatile memory 2465 mayinclude a program 2466 (e.g., in the form of program code orcomputer-executable instructions for performing operations) andcalibration tables 2468. In operation, the controller 2360 may receivethe program 2466 and may synchronize the functions of thecapacitance-to-digital converter 2321 and the display circuit 2325 (seeFIG. 23). The non-volatile memory 2465 receives and stores the program2466 as well as LUT and calibration tables 2468. The program 2466 caninclude a number of suitable algorithms, such as, for example, aninitialization algorithm, a calibration algorithm, a pattern-matchingalgorithm, a multiplexing algorithm, a display management algorithm, anactive sensor activation algorithm, and a non-active sensor managementalgorithm.

FIG. 25 illustrates a routing of sensor plate traces 2535 of an obscuredfeature detector, according to one embodiment. In the illustratedembodiment of FIG. 25, each of the sensor plate traces 2535 hassubstantially similar trace length and the sensor plate traces 2535 aresurrounded by an active shield trace 2536. In some embodiments, as shownin FIG. 25, each of the sensor plate traces 2535 is shielded on one orboth sides with the active shield trace 2536. In some embodiments theactive shield trace 2536 is routed at a uniform distance from the sensorplate traces 2535 on both sides of each sensor plate trace 2535. In someembodiments, the active shield traces 2536 are substantially parallel tothe sensor plate traces 2535. In some embodiments, the active shieldtraces 2536 are positioned such that the active shield traces 2536shield the sensor plate traces 2535 from external electromagneticfields. In some embodiments, the sensor plate traces 2535 and activeshield traces 2536 are positioned such that the capacitance between eachsensor plate trace 2535 and each respective active shield trace 2536 issubstantially the same for each sensor plate trace 2535 and itsrespective active shield trace 2536. In some embodiments a sensor platetrace 2535 is accompanied by two active shield traces 2536, such thatone active shield trace 2536 is positioned on each side of the sensorplate trace 2535. In some embodiments, a sensor plate trace 2535 and anactive shield trace 2536 are positioned such that there is a constantdistance between a sensor plate trace 2535 and the respective activeshield trace 2536, along their length. In some embodiments each of theactive shield traces 2536 is positioned at a uniform distance away fromthe respective sensor plate trace 2535. In some embodiments a segment ofeach sensor plate trace 2535 and a segment of each active shield trace2536 comprise copper traces on a PCB. In some embodiments, the sensorplate traces 2535 and active shield traces 2536 are both located on thesame layer of a PCB. In some embodiments, the active shield traces 2536are driven at a fixed voltage level. In some embodiments, the activeshield traces 2536 are driven at a voltage that is similar to thevoltage driven on the sensor plate traces 2535.

In some embodiments the active shield traces 2536 may be routed at adistance of approximately 0.6 mm from each sensor plate trace 2535,along as much of the length of the sensor plate trace 2535 as ispossible. In some embodiments the sensor plate traces 2535 areapproximately 0.15 mm wide throughout one segment of the sensor platetrace 2535.

In some embodiments a shield is configured such that there is a shieldlayer above each sensor plate trace 2535 and a shield layer below eachsensor plate trace 2535. A shield layer in some embodiments is a layerof copper on an adjacent layer of a PCB. As a result the sensor platetraces 2535 may shield both on a layer above the sensor plate traces2535 and on a layer below the sensor plate traces 2535, as well asshielding on either side of the sensor plate traces 2535. In someembodiments the shielding above the sensor plate trace 2535, below thesensor plate trace 2535, and on either side of the sensor plate trace2535 are all electrically coupled to each other.

In some embodiments the shield is an active shield. An active shield isa shield that is driven with the same voltage potential as the sensedsensor plate(s). In some embodiments the voltage wave that is driven onthe sensor plates 2505 and shield may have a triangular shape. In someembodiments the voltage wave that is driven on the sensor plates 2505and shield may have a sinusoidal shape. In some embodiments the voltagethat is driven on the sensor plates 2505 and shield may have a differentwave shape.

Presently available obscured feature detectors may include sensor platetraces to connect a sensing circuit to sensor plates. In some presentlyavailable obscured feature detectors no shielding is used to shield thesensor plate traces from interferences. These detectors may beconfigured to keep potential interferences a safe distance away from thesensor plate traces.

Other presently available obscured feature detectors may have shieldingwhich may shield the sensor plate traces for a portion of the length ofthe sensor plate trace. In some presently available obscured featuredetectors up to 82% of the sensor plate trace's length may be shielded.An example of a presently available obscured feature detector withshielding is shown in FIG. 38. In presently available obscured featuredetectors with shielding, a trace may be routed such that there is aground plane on a PCB layer that is beneath the sensor plate trace and avia that connects the segment of the sensor plate trace that is on thetop layer of the PCB with a segment of the sensor plate trace that is ona lower layer of the PCB. For the segment of the sensor plate trace thatis on a lower layer of the PCB, there is a first active shield plane ona layer of the PCB above the sensor plate trace and a second activeshield plane on a PCB layer below sensor plate trace. The first activeshield plane, the second active shield plane, and the shield traces areall coupled together and are all driven as an active shield. The activeshielding may comprise up to 82% of the length of the sensor platetrace.

In these presently available obscured feature detectors, the materialthat is between the trace and the ground plane may absorb humidity. Thematerial under some of the traces may absorb more humidity than thematerial that is under other traces. As a result, exposure to humiditymay cause the relative sensor readings of the sensor plate traces tochange. In other words, when exposed to humidity some of the sensorreadings may change more than other sensor plate sensor readings, as aresult of the humidity. Undesirably, the change is the result of thehumidity being absorbed between the trace and ground—not as a result ofan obscured feature being present.

The present disclosure provides improved obscured feature detectors withshielding that may shield the sensor plate traces for more than 82% ofthe length of the sensor plate trace.

FIG. 25 also illustrates an improved method of routing the sensor platetraces 2535 that may result in better performance. In FIG. 25 there is avery short sensor plate trace 2535 that connects the sensing circuit2527 to a via 2534. This sensor plate trace 2535 may be only one or twomillimeters long. It is made as short as is practicably possible. Thevia 2534 connects the segment of the sensor plate trace 2535 that is onthe top layer of the PCB with a segment of the sensor plate trace 2535that is on a lower layer of the PCB. For the segment of the sensor platetrace 2535 that is on a lower layer of the PCB, there is a first activeshield plane 2537 on a layer of the PCB above the sensor plate trace2535 and a second active shield plane 2538 on a PCB layer below sensorplate trace 2535. The first active shield plane 2537, the second activeshield plane 2538, and the shield traces are all coupled together andare all driven as an active shield.

When the sensor plate trace 2535 and the active shield trace 2536 areboth driven with the same signal, then they are the same voltagepotential, and the capacitance between them may become unimportant. As aresult, as the PCB absorbs humidity and the dielectric constant of thePCB changes, these changes in the dielectric constant of the PCB may nothave an effect upon the sensor readings. Changes in the capacitancebetween the sensor plate trace 2535 and the active shielding (e.g., theactive shield trace 2536) do not affect the sensor readings. The resultmay be that the sensor plate traces 2535 are able to maintain theircalibration values better, and the obscured feature detector may be ableto determine the locations of the obscured features better.

FIG. 26 is a diagram of sensor plate configuration of an obscuredfeature detector, according to one embodiment. In this illustratedarrangement each of the eleven different sensor plates 2605 have similarprimary sensing field zones. FIG. 26 illustrates a sensor plate group2607 that includes eleven sensor plates 2605 and an active shield plate2623. In this embodiment the group 2607 of eleven sensor plates 2605 areon a bottom layer (e.g., a fourth layer) of a PCB. In this embodimentthe active shield plate 2623 covers the entire third layer of the PCB.In some embodiments, one sensor plate 2605 may be sensed at a time. Insome embodiments when one sensor plate 2605 is sensed, all of the sensorplates 2605, including the active shield plate 2623, are driven with thesame signal as the sensed sensor plate 2605. The group 2607, plus theactive shield plate 2623, when driven together may push the field linesdeeper into the sensed surface than may be possible if just a singlesensor plate 2605 was driven. In some embodiments this allows fieldlines from a single sensor plate 2605 to penetrate more deeply, andallows a single sensor plate 2605 to sense more deeply, than may bepossible if a single sensor plate 2605 were driven alone.

In the embodiment of FIG. 26, the sensing field may be created by thecombination of the group 2607 and the active shield plate 2623 when theyare both driven with the same signal. In this embodiment thesimilarities in the configuration of each of the eleven sensor plates2605 may provide each sensor plate 2605 with primary sensing zones thatare geometrically similar. Likewise, each of the sensor plates 2605 mayalso have similar sensing fields within its respective primary sensingfield zones.

The configuration of the sensor plates 2605 and the active shield plate2623 in FIG. 26 helps provide similar primary electric field zones foreach of the sensor plates 2605. Each of the eleven sensor plates 2605has a similar external border 2611. They also each have a similar areaand a similar internal border 2610. They also each have similarelectrical surroundings. Each sensor plate 2605 is surrounded on eitherside by either another sensor plate 2605 or the active shield plate2623. Both the active shield plate 2623 and adjacent sensor plates 2605may be driven similarly, and as a result they may each provideequivalent electrical surroundings. The result may be that each of theeleven sensor plates 2605 in FIG. 26 has a primary sensing field zonethat is geometrically similar.

The shapes of the eleven the sensor plates 2605 in FIG. 26 are notidentical. Although it may be ideal for the sensor plates 2605 to beidentical, an adjustment was made to four of the sensor plates 2605 (twosensor plates 2605 at each end), so that more similar primary sensingfield zones may be obtained. In this embodiment achieving moreequivalent primary sensing field zones may be more desirable than havingidentical sensor plate geometries. Nevertheless, all of the elevensensor plates 2605 may have substantially the same area, same externalborder 2611, similar internal border 2610 configuration, and similarelectrical surroundings. This configuration with these similarities maygive each sensor plate 2605 an equivalent primary sensing field zone.

In some embodiments it may be beneficial to have similar electricalsurroundings that extend beyond the internal borders 2610 of a sensorplate 2605 for 1× to 1.5× the desired sensing depth. For example, if a1-inch sensing depth is desired it may be beneficial to have similarelectrical surroundings around each sensor plate 2605 for at least 1inch to 1.5 inches beyond the internal borders 2610 of each sensor plate2605.

FIG. 27 is a cross-sectional view of an obscured feature detector,according to one embodiment, including a housing 2719, with light pipes2708 and a button 2724, and a PCB 2740. In some embodiments, as shown inFIG. 27, a housing 2719 comprises an upper housing, an on-off switch2724, a handle 2714, a plurality of light pipes 2708, and a power supplycompartment. In some embodiments a conforming core (see conforming coreapparatus 3449 in FIG. 34) may be configured to flexibly couple thehousing 2719 to a sensor plate board 2740. In some embodiments thesensor plate board 2740 is a multi-layered PCB with a top layer 2744, asecond layer 2743, a third layer 2742, and a bottom layer 2741. In someembodiments the sensor plate board 2740 is a multi-layered PCB thatcouples a capacitance-to-digital converter 2321, a display circuit 2325,and a controller 2360, as described above with reference to FIG. 23. Insome embodiments, the housing 2719 comprises plastic. In someembodiments, the housing 2719 comprises ABS plastic. In some embodimentsa conductive hand guard 2756 shields the user's hand from the sensorplate board 2740. In some embodiments the hand guard 2756 is connectedto the ground of a sensing circuit.

In some embodiments, the handle 2714 comprises a gripping surface. Insome embodiments a portion of the gripping surface comprises anelastomer that makes the handle 2714 easier to grip. The handle 2714 ispreferably positioned so that the user's hand does not obscure a view ofthe indicators 2706 when grasping the handle 2714. In some embodiments,the power supply compartment comprises a cavity for holding a suitablepower supply, such as batteries, and a battery cover for accessing thecompartment.

In some embodiments the hand guard 2756 may be configured so that thereare no significant straight-line paths between the sensor plates and theuser's hand. In some embodiments the housing 2719 may be composed of anelectrically conductive material which may comprise the hand guard 2756.In some embodiments the conductive layer of material of the hand guard2756 may be a layer of conductive plastic. In some embodiments theconductive layer of material of the hand guard 2756 may be a layer of adifferent conductive material, such as a conductive paint. In someembodiments the conductive layer of material of the hand guard 2756 maybe a sheet of metal that is hidden within the housing 2719. In someembodiments the hand guard 2756 may comprise tin-plated steel, which mayprovide for quick, easy and reliable solder joints. In some embodimentsan entire layer of a PCB may comprise the hand guard 2756. In someembodiments only a portion of a layer of a PCB may comprise the handguard 2756, because in some embodiments it may not be necessary for thehand guard 2756 to comprise an entire layer. For example, a ring aroundthe outside of a PCB may be an effective hand guard 2756.

In some embodiments the hand guard 2756 is configured to minimize aneffect of a size and position of the hand. In some embodiments the handguard 2756 is positioned so that it is near the hand because in someembodiments it may be most effective when it is nearest to the hand. Insome embodiments the hand guard 2756 may be electrically coupled to theground of a sensing circuit 2327 (see FIG. 23). In some embodiments thehand guard 2756 may be coupled to the voltage of the sensing circuit2327. In some embodiments a different electrically conductive point ofthe sensing circuit 2327 may be electrically coupled to the hand guard2756. In some embodiments an electrical wire comprises the electricalpath between the hand guard 2756 and the sensing circuit 2327.

FIG. 28 illustrates a sensor plate group 2801 with four sensor plates2805. In some embodiments, as shown in FIG. 28, the sensor plate group2801 may comprise four similar sensor plates 2805. In the embodimentshown in FIG. 28, each triangular sensor plate 2805 has two sides of atriangle that each form internal borders 2810 and one side of thetriangle that forms an external border 2811. The four sensor plates 2805in FIG. 28 are each radially symmetrical. From these four sensor plates2805, three different sensing zones may be possible. For example, if avertical stud were disposed at some arbitrary position relative to thesensor plates 2805, three different readings might appear, each readingrelative to one sensing zone of the three zones. The first zone mightcorrespond to the sensor plate on the left. The second zone mightcorrespond to the top and bottom sensor plates (e.g. as can beappreciated, the top and bottom sensor plates would have the samereading because they would each sense the same portion of the verticalstud.) The third zone might correspond to the right sensor plate. Therelative readings for each of the three zones could be used to determinethe location of the vertical stud.

FIG. 29 illustrates a sensor plate group 2901 with six sensor plates2905. In some embodiments, as shown in FIG. 29, the sensor plate group2901 may include six similar sensor plates 2905. In the embodiment shownin FIG. 29, each sensor plate 2905 has two straight sides that each forminternal borders 2910 and a straight side that forms an external border2911. In some embodiments each of the sensor plates 2905 havesubstantially the same area.

FIGS. 30-32 are views of a prior art obscured feature detector. In priorart obscured feature detectors a set of identical sensor plates 3005 aretypically arranged in a linear fashion, such as shown in FIGS. 30, 31,32, and 33. FIG. 30 is a prior art obscured feature detector 3001 placedon a comparatively thinner surface 3012. FIG. 31 is the prior artobscured feature detector 3001 placed on a comparatively thicker surface3113. FIG. 32 shows a side view of the prior art obscured featuredetector 3001, illustrating primary sensing field zones 3215, 3216, 3217for several sensor plates 3005, including sensor plates A, B, C, D, E.FIG. 33 shows an elevation view of a bottom surface of the prior artobscured feature detector 3001, illustrating the primary sensing fieldzones 3215, 3216, 3217 for sensor plates A, B, C, D, E.

Referring generally and collectively to FIGS. 30-33, each of the sensorplates 3005 performs a sensor reading of a surface to detect an obscuredfeature behind the surface. The sensor readings are then compared. Thesensor plates 3005 that have the highest sensor readings are interpretedto be the locations of obscured features. However, as shown in FIGS. 30and 31, the sensor plates 3005 that are near the ends of the group maynot respond to obscured features in the same manner as the sensor plates3005 that are near the center. This issue may be particularly evidentwhen the prior art obscured feature detector 3001 is moved from thethinner, or less dense, surface 3012 to an thicker, or more dense,surface 3113.

FIG. 30 shows representative sensor readings of the prior art obscuredfeature detector 3001 that is placed on the relatively thinner surface3012. The relatively thinner surface 3012 could be 0.375-inch-thicksheetrock. FIG. 31 shows representative sensor readings of the prior artobscured feature detector 3001 that is placed on a relatively thickersurface 3113. The relatively thicker surface 3113 could be0.625-inch-thick sheetrock.

In FIG. 30, the prior art obscured feature detector 3001 is placed onthe relatively thinner surface 3012. Each of the sensor plates 3005 mayhave a calibration adjustment so that each has a calibrated reading of,for example, 100. If this same prior art obscured feature detector 3001is then moved to another surface 3113 that is thicker, or to a surfacethat has a higher dielectric constant, the sensor readings would change.An image of the same prior art obscured feature detector 3001 on thethicker surface 3113 is shown in FIG. 31. Ideally, each of the sensorplates 3005 on the thicker surface 3113 would have similar sensorreadings to each other, because they are all on the same thicker surface3113, with no obscured features present. However, it may be observedthat the sensor readings of the sensor plates 3005 near the ends may seea larger reading increase than the sensor plates 3005 near the center.In FIG. 31, it may be seen that the sensor plates 3005 near the centerhave sensor readings of 200, but the sensor plates 3005 at the ends havesensor readings of 250.

In the prior art obscured feature detector 3001 of FIG. 31, and otherprior art obscured feature detectors, the sensor plates 3005 that are atthe ends are alone in creating electric fields 3009 that extend beyondthe edges of the group of sensor plates 3005. As a result, the sensorplates 3005 near the end may respond with a disproportionately higherreading when placed on a thicker surface 3113. Disadvantageously, thecontroller 2360 may have difficulty determining if the elevated sensorreadings are due to the presence of an obscured feature, or due to theprior art obscured feature detector 3001 being placed on the thickersurface 3113. The disclosed embodiments may address these and otherchallenges.

FIG. 32 illustrates the field lines for the prior art obscured featuredetector 3001 of FIGS. 30 and 31. FIG. 32 shows a group of sensor plates3005 and also shows a two-dimensional representation of the field linesfor each of the sensor plates 3005. The field lines are shown forillustrative purposes and are a representation of the actual sensingfield. The field lines drawn are equipotential electric field lines.However, this drawing does not limit the scope of the disclosure to thistype of field alone. Vector electric field lines or magnetic field linescould have been illustrated in the drawing and are within the scope ofthe disclosure. The sensing field may be an electric field, a magneticfield, or an electromagnetic field, which is a combination of anelectric field and a magnetic field.

In FIG. 32 there are thirteen sensor plates 3005. All of the sensorplates 3005 may be driven with the same signal simultaneously, while onesensor plate 3005 at a time is sensed. Because the sensor plates 3005are driven simultaneously, with the same signal, the sensing field isdefined by the field created by the group of sensor plates 3005, asillustrated in FIG. 32. An active shield plane is not illustrated in thefigure, but an active shield may contribute to the sensing field in someembodiments. Five of the sensor plates 3005 are labeled A, B, C, D, E.The field lines emanating from sensor plate E are primarily parallel tosensor plate E. However, the field lines emanating from sensor plate Aare not very parallel to sensor plate A. Because the field lines do nothave similar direction and strength at each point within the primarysensing field zone the sensor plates A and E do not have similar sensingfields within their primary sensing field zones.

In contrast, sensor plate D and sensor plate E have similar primarysensing field zones because the volume of the sensing field where theyare able to sense effectively and the sensing field within that primarysensing field zone are similar. The sensing fields within a primarysensing field zone are similar if the direction of the sensing field andstrength of the sensing field are similar at each point within theprimary sensing field zone.

FIG. 33 illustrates the same concept from a different angle orperspective. In FIG. 33 the five sensor plates 3005 are again labeled A,B, C, D, E. The approximate primary sensing field zones for each of thesensor plates 3005 are highlighted. On the two-dimensional drawing ofFIG. 33, the primary sensing field zone 3215 for sensor plate A isindicated by the drawing of the sensing field lines for sensor plate A.On the two-dimensional drawing of FIG. 33, the primary sensing fieldzone 3216 for sensor plate B is indicated by the drawing of sensingfield lines for sensor plate B. On the two-dimensional drawing of FIG.33, the primary sensing field zone 3217 for sensor plate C is indicatedby the drawing of sensing field lines for sensor plate C.

FIGS. 32 and 33 illustrate the primary sensing field zone with atwo-dimensional drawing. However, in reality a three-dimensional primarysensing field zone may exist. There may be a three-dimensional zone foreach sensor plate 3005 that comprises the primary sensing field zone foreach given sensor plate 3005. In contrast to the prior art embodiment ofFIGS. 32 and 33, in some embodiments of the present disclosure thesensor plates 3005 may have an equivalent primary sensing field zone.Each sensor plate 3005 in a group that has an equivalent primary sensingfield zone may have an equivalent response to change in surfaces. Thisdisclosure illustrates some configurations wherein each sensor plate3005 in a group may have an equivalent primary sensing field zone. Insome embodiments each sensor plate 3005 with a similar primary sensingfield zone may have a similar change in sensor readings in response to achange in the detected surface. In some embodiments the sensor plates3005 in a group of sensor plates 3005 are each radially symmetrical.

FIG. 34 illustrates a diagrammatic side view of a chassis of aconforming core apparatus 3449 of a surface-conforming obscured featuredetector, according to one embodiment. FIG. 35 is a perspective view ofthe chassis of the conforming core apparatus 3449 of FIG. 34.

The present disclosure provides various embodiments of asurface-conforming obscured feature detector. Conventional detectorshave sensor plates 2205 that are rigidly connected together, and as aresult the size of obscured feature detectors typically remainsrelatively small to function on the curved surfaces that are typical ofmany architectural surfaces. The surface-conforming obscured featuredetectors disclosed herein conform to the contour of a surface, minimizeair gaps, and are able to be larger feature detectors that can offer avariety of performance improvements. The improvements described in thepresent disclosure are applicable to both conventional detectors thatare relatively small and to larger feature detectors.

In some embodiments, the obscured feature detector has one or moreflexible PCBs, such as a sensor plate board 2740, that can bend to matchthe contour of the surface to be detected. The flexible PCBs comprise aflexible substrate. Other flexible substrates can also be used that canbe made of wood, paper, plastic, or other flexible materials. Rigid flexPCBs can also be used.

The one or more PCBs can be flexibly connected to the housing 2019 usinga flexible medium such as foam rubber, springs, gel, hinges, pivotpoints, an encapsulated fluid such as air, or other suitablecompressible or flexible media. In some embodiments the housing 2019 isable to flex. In some embodiments the housing 2019 is partiallyflexible. In some embodiments the housing 2019 has integrated plasticleaf springs or other types of springs or features that provideflexibility. In some embodiments of the obscured feature detector 2001,the sensor plates 2205 can be mounted on a PCB that is mounted externalto the housing 2019. In some embodiments the PCB is connected to thehousing 2019 via a foam rubber ring. In some embodiments, the foamrubber ring is about 7 mm thick and is formed approximately in the shapeof a ring that is about 6 mm wide along the long side and about 5 mmthick along the short side, and approximately follows the perimeter ofthe housing 2019. A permanent adhesive, such as a pressure sensitiveacrylic adhesive, can be used to bond the foam rubber ring to thehousing 2019 and to the PCB.

In some embodiments, the foam rubber ring is compressible and the PCB isflexible, allowing the obscured feature detector 2001 to conform tocurvature and irregularities of the surface 2002 against which it isplaced. A variety of flexible and/or compressible materials can besuitable for the flexible medium. Ethylene propylene diene monomer(EPDM) foam rubber that is rated for 25% compression under about 1.5pounds per square inch of pressure can be used. Other types of foamrubber such as polyurethane foam or silicon rubber foam can also beused. In some embodiments it is desirable that the flexible mediumattached between the PCB substrate and the housing 2019 not beelectrically conductive or partially conductive, at least not to theextent that it would interfere with operation of the obscured featuredetector 2001.

In some embodiments, the conforming core apparatus 3449, such as shownin FIGS. 34 and 35, can flexibly connect the housing 2019 to the PCB. Insome embodiments the conforming core apparatus 3449 may have two or morepivots 3452. In some embodiments the pivots 3452 are flexible joints. Insome embodiments the pivots 3452 are ball joints. In some embodimentsthe pivots 3452 are hinges. In some embodiments the pivots 3452 areliving hinges. A living hinge is a thin flexible hinge made from thesame material as the two rigid pieces it connects. In some embodimentsthe pivots 3452 may be any of many other flexible mechanisms.

In some embodiments the conforming core apparatus 3449 comprises a mainshaft 3453, as illustrated in FIGS. 34 and 36. In some embodiments themain shaft 3453 comprises a shaft member. In some embodiments the mainshaft 3453 comprises a shaft member and two pivots 3452. In someembodiments each pivot 3452 of the main shaft 3453 couples the mainshaft 3453 to a minor shaft 3454. In some embodiments each minor shaft3454 comprises a shaft member and three pivots 3452. In some embodimentsof the minor shaft 3454 there is one pivot 3452 near the center of eachminor shaft 3454 and there are two additional pivots 3452, one at eachend of the minor shaft 3454. In some embodiments there are four feet3455 coupled to the main shaft 3453. In some embodiments each foot 3455has a pivot 3452. In some embodiments the pivots 3452 at each of theends of the two minor shafts 3454 are coupled to a pivot 3452 in each ofthe four feet 3455. In some embodiments each foot 3455 is coupled to thePCB. In some embodiments the PCB can flex to match the contour of thesurface 2002.

In some embodiments the feet 3455 couple the PCB to the minor shaft 3454as shown in FIGS. 34 and 35.

In some embodiments the conforming core apparatus 3449 comprises themain shaft 3453, two minor shafts 3454, and four feet 3455. In someembodiments there are six pivots 3452 in the conforming core apparatus3449. In some embodiments there are more than six pivots 3452. In someembodiments there are less than six pivots 3452.

In some embodiments, as shown in FIG. 35, all of the pivots 3452 areliving hinges, such that the entire conforming core apparatus 3449comprises one single piece of injection molded plastic.

FIG. 36 is a flow diagram of a method 3600 of detecting an obscuredfeature behind a surface, according to one embodiment. A firstoperation, as illustrated in the flow diagram in FIG. 36, may be toinitialize 3602 a detector, which may involve running an initializationalgorithm. The detector may be according to one of the embodimentsdescribed herein. After initialization, the sensor plates may be read3604. In some embodiments each of the sensor plates may be read multipletimes, each time using a different configuration. The differentconfigurations may comprise different drive currents, different voltagelevels, different sensing thresholds, or other different configurationparameters. Each of these readings of the sensor plates may be referredto as native readings. In some embodiments multiple native readings maybe added together to comprise a reading. In some embodiments there maybe a separate reading for each sensor plate.

In some embodiments, each of these readings has a calibration 3606adjustment performed that is achieved by adding a predeterminedcalibration value to each reading. In some embodiments, aftercalibration, the readings for each of the sensor plates would be thesame if the detector were to be placed on a uniform surface.

In some embodiments, the largest sensor plate reading is compared 3608to the lowest sensor plate reading. The difference is then compared 3608to a threshold value. In some embodiments, if the difference is lessthan a predetermined threshold value, then all of the indicators may beturned off 3610, to indicate that no stud is present. If the differenceis larger than a predetermined threshold value, then a determination maybe made as to which indicators to activate. In certain embodiments, thereadings may be scaled 3612 to a predetermine range, which may involvesetting the lowest value to a number such as 0 and scaling the largestreading to a value such as 100. Then all of the intermediate valueswould be scaled proportionately. The scaled readings may then becompared 3614 to predetermined patterns which are scaled in a similarfashion.

In some embodiments there may be a set of predetermine patterns. The setof predetermined patterns may correspond to different combinations ofhidden features that the detector may encounter. For example, the set ofpredetermined patterns may correspond to different positions for asingle stud. In some embodiments, the set of predetermined patterns mayinclude positional combinations of two studs. A pattern matchingalgorithm may be employed to determine which predetermined pattern bestmatches the reading pattern. The detector may then activate 3616 theindicators that correspond to the best matching predetermined pattern.

In other embodiments, after calibrating the sensor plate readings, adetermination is made if an obscured feature is present. The lowestsensor plate reading may be subtracted from the highest sensor platereading. If the difference is greater than a threshold value, then adetermination is made that an obscured feature is present. If it isdetermined that no obscured features are present, then all of theindicators may be deactivated. If an obscured feature is present then aprocess may begin to determine position(s) and/or width(s) of theobscured feature(s). In some embodiments, all of the current sensorplate readings may be scaled such that the lowest reading is scaled to apredetermined value (such as 0) and the maximum reading is scaled to asecond predetermined value (such as 100). All intermediate values may bescaled proportionately. Scaled readings may be easier to compare to aset of predetermined patterns.

FIG. 37 illustrates two different PCBs in a stacked configuration,according to one embodiment of the present disclosure. A sensor plateboard 3740 and an interconnection board 3751 may be stacked on top ofone another and bonded to each other. The sensor plate board 3740 mayinclude one or more sensor plates. The interconnection board 3751 mayinclude the plurality of indicators 3706. The sensor plate board 3740and/or the interconnection board 3751 may be PCBs or otherwiseintegrated into a PCB. In some embodiments the bonding agent that bondsthe two PCBs 3740, 3751 together may be solder. In some embodimentssolder paste may be used to bond the two PCBs 3740, 3751 together. Insome embodiments, they may be bonded together with solder and theprocess to bond them together may be standard SMT processes. The SMTprocess may include placing one PCB on top of another. In someembodiments, pins may be used to ensure proper alignment of the two PCBs3740, 3751. In some embodiments the final step of the SMT process mayinvolve running the stacked PCBs 3740, 3751 through a reflow oven.

In other embodiments, both the sensor plates and the circuitry may beassembled on a single PCB. A 1.6-mm-thick PCB with four layers of coppercan be used. In some embodiments the first layer of copper is on theupper surface and all of the electrical components are soldered to thislayer. The second layer of copper can be at a position that is about0.35 mm below the first layer of copper, such that there is about 0.35mm of PCB substrate between the first and second layers of copper. Thethird layer of copper can be at a position that is about 0.1 mm belowthe second layer of copper, such that there is about 0.1 mm of PCBsubstrate between the second and third layers of copper. A fourth layerof copper can be at a position that is about 0.35 mm below the thirdlayer of copper, such that there is about 0.1 mm of PCB substratebetween the third and fourth layers of copper. In some embodiments viascan be drilled to selectively connect the four layers of copper.

In some embodiments a final layer of substrate material that is 0.8 mmthick can be placed to cover the fourth layer of copper. In someembodiments, no holes are drilled through the 0.8-mm-thick layer ofsubstrate. The 0.8-mm-thick layer of substrate may help protect thecircuit from electrostatic discharge. Alternatively, a layer of plastic,or other non-conductive material, can be used to shield the circuit fromelectrostatic discharge and to physically protect the PCB. In someembodiments, a layer of plastic can be used in addition to a protectivelayer of circuit board substrate. It is to be understood that the layersand thicknesses indicated here are only exemplary of one embodiment.Other combinations of layers and thicknesses, and materials, can also beused.

In some embodiments the sensor plates can be placed on the fourth layerof copper. A shield to electrically protect the sensor plates fromelectrical interference from ambient conditions, including the user'shand, may be used. In some embodiments the shield may be placed on thefirst layer of copper. In some embodiments, a solid shield may coversubstantially all of the shield's area, instead of using a mesh,stripes, or another pattern that may provide less than substantially allof the shield's area.

In some embodiments the electrically conductive paths that link thesensor plates to the capacitance-to-digital converter comprise sensorplate traces. In some embodiments the sensor plate traces are placedprimarily on the second layer of copper, and shields for the signals areplaced on the first and fourth layers of copper.

In some embodiments, the interconnection boards 3751 that are solderedto the sensor plate board 3740 are covered with a layer of epoxy, a globof epoxy, or another conformal coating which may improve the reliabilityof solder joints. In some embodiments the interconnection boards 3751 onthe sensor plate board 3740 are wire bonded to the PCB withchip-on-board technology. The chip-on-board technology may involve thesteps of (1) attaching bare die to the PCB, (2) wire bonding(electrically connecting signals on the bare die to the PCB), and (3)covering the bare die and wire bonds with a coating of epoxy or otherappropriate material. The chip-on-board technology may improve thereliability of solder joints.

In some embodiments integrated circuits that have packages with externalleads are used such as QFP packages, TSOP packages, SOIC packages, QSOPpackages, or others. Components that have external leads may improvesolder joint reliability.

FIG. 38 illustrates a prior art configuration for routing and shieldingsensor plate traces 3835 from the controller of a sensing circuit 3827to sensor plates 3805. In this prior art, the sensor plate trace 3835 isrouted such that there is a ground plane 3833 on a PCB layer that isbeneath the sensor plate trace 3835. A via 3834 connects the segment ofthe sensor plate trace 3835 that is on the top layer of the PCB with asegment of the sensor plate trace 3835 that is on a lower layer of thePCB. For the segment of the sensor plate trace 3835 that is on a lowerlayer of the PCB, there is a first active shield plane 3837 on a layerof the PCB above the sensor plate trace 3835 and a second active shieldplane 3838 on a PCB layer below sensor plate trace 3835. The firstactive shield plane 3837, the second active shield plane 3838, andshield traces 3836 are all coupled together and are all driven as anactive shield. In the prior art the active shielding may comprise up to82% of the length of the sensor plate trace 3835.

In these prior art detectors, the material that is between the sensorplate trace 3835 and the ground plane 3833 may absorb humidity. Thematerial under some of the sensor plate traces 3835 may absorb morehumidity than the material that is under other sensor plate traces 3835.As a result, exposure to humidity may cause the relative sensor readingsof the sensor plate traces 3835 to change. In other words, when exposedto humidity some of the sensor plate 3805 sensor readings may changemore than other sensor plate 3805 sensor readings, as a result of thehumidity. Undesirably, the change is the result of the humidity beingabsorbed between the sensor plate trace 3835 and ground—not as a resultof an obscured feature being present. Improved obscured featuredetectors, according to the present disclosure, may shield the sensorplate traces 3835 for more than 82% of the length of the sensor platetrace 3835.

FIG. 39 is a cross-sectional view of an obscured feature detector 3901,according to another embodiment, illustrating electric field patterns.FIG. 39 shows an orientation of the electric field lines 3904, 3905according to previously mentioned embodiments, where the electric fieldlines 3904, 3905 curve around the side of the obscured feature detector3901. FIG. 39 shows an obscured feature detector 3901 that has theelectric field lines 3904, 3905 extending from the sensor plates 3908and ending on a common plate(s) 3906, 3907. There the sensor plates 3908are located on the bottom of the obscured feature detector 3901 and thecommon plate(s) 3906, 3907 is located on the sides of the obscuredfeature detector 3901. A shielding plate 3909 (e.g. an active shield) isdisposed between the sensor plates 3908 and the common plate(s) 3906,3907, causing the electric field lines 3904, 3905 to extend down,outward, and up around the sides of the obscured feature detector 3901.

The common plate(s) 3906, 3907 may comprise a single plate or a numberof different plates that are electrically connected, thereby maintaininga uniform voltage while extending along various sides of the obscuredfeature detector 3901. To ensure that the electric field lines 3904,3905 do not extend in a straight line from the sensor plates 3908 to thecommon plate(s) 3906, 3907 or otherwise penetrate the obscured featuredetector 3901, a shielding plate 3909 may be positioned between thesensor plates 3908 and the common plate(s) 3906, 3907. The shieldingplate 3909 may hold the same charge or voltage as the sensor plates 3908so that the capacitance between them may become unimportant. If theshielding plate 3909 has the same voltage or charge as the sensor plates3908, the electric field lines 3904, 3905 coming from the sensor plates3908 will not be drawn to the shielding plate 3909, and will curvearound it in order to reach a plate with a different potential such asthe common plate(s) 3906, 3907. The shielding plate 3909 may bepositioned advantageously to cause the electric field lines 3904, 3905to be directed around the edges or sides of the obscured featuredetector 3901. For example, in some embodiments the shielding plate 3909may be located on a layer directly above the sensor plates 3908 andcover the entire area of the sensor plates 3908. In some embodiments,the shielding plate 3909 may then extend around the ends (or extremes)of the sensor plates 3908 and lower itself until the portion of theshielding plate 3909 that extends beyond the area of the sensor plates3908 lies on the same plane as the sensor plates 3908. The portion ofthe shielding plate 3909 that is on the same plane as the sensor plates3908 may then extend to the extreme ends of the obscured featuredetector 3901, thereby forming a lip 3910 around the sensor plates 3908.Ideally, the shielding plate 3909 would cause the electric field lines3904, 3905 to reach from the sensor plates 3908 to the common plate(s)3906, 3907 only by curving around the sides of the obscured featuredetector 3901.

In some applications, it may be desirable to have the electric fieldlines 3904, 3905 diverge from the obstructed feature detector 3901 suchthat they circle around the side of the obscured feature detector 3901.If the electric field lines 3904, 3905 are allowed to curve around thesides of the obscured feature detector 3901, they may be able topenetrate further into a surface than were they confined to the areadirectly in front of the sensor plates, which may cause the sensorplates 3908 to yield more accurate or consistent readings. In someapplications, it may be desirable to sense around the sides of theobscured feature detector 3901, rather than only directly in front ofthe sensor plates 3908.

FIG. 40 is a cross-sectional view of an obscured feature detector 4001,according to another embodiment, illustrating electric field patterns.FIG. 40 shows an orientation of the electric field lines 4004, 4005curving out and up and around the sides of the obscured feature detector4001. The obscured feature detector 4001 includes a housing 4019, and asensor plate board 4040 (e.g., a PCB). In some embodiments, the housing4019 may comprise an upper housing, an on-off switch 4024, a handle4014, and a plurality of light pipes 4018. The sensor plate board 4040may be a multi-layered PCB with a top layer 4044, a second layer 4043, athird layer that may be an active shield 4009, and a bottom layer thatincludes sensor plates 4008. Additional components of the sensor plateboard 4040 may include components described above with reference to FIG.23.

FIG. 40 shows an obscured feature detector 4001 that forms electricfield lines 4004, 4005 extending from sensor plates 4008 and ending onone or more common plates 4006. The sensor plates 4008 are positioned onthe bottom of the obscured feature detector 4001 and the one or morecommon plates 4006 are located on a different plane from the sensorplates 4008, to be positioned a greater distance from a surface throughwhich the obscured feature detector 4001 may be detecting an obscuredfeature. The common plate(s) 4006 may comprise a single plate or anumber of different plates that are electrically connected, therebymaintaining a uniform voltage. A shielding plate 4009 (e.g. an activeshield) is disposed between the sensor plates 4008 and the commonplate(s) 4006. Electric fields (represented by electric field lines4004, 4005) form between the sensor plates 4008 and the common plate(s)4006, and the shielding plate 4009 causes the electric field lines 4004,4005 to extend down, outward, and up around the sides of the obscuredfeature detector 4001. Stated otherwise, the shielding plate 4009restricts the electric field lines 4004, 4005 from extending in astraight line from the sensor plates 4008 to the common plate(s) 4006,4007.

The shielding plate 4009 may be and active shield driven at the samecharge or voltage as the sensor plates 4008 so that the capacitancebetween the shielding plate 4009 and the sensor plates 4008 may benominal and non-impactful to the sensing of the sensor plates 4008. Ifthe shielding plate 4009 has the same voltage or charge as the sensorplates 4008, the electric field lines 4004, 4005 generated from thesensor plates 4008 will not be drawn to the shielding plate 4009, andwill curve around it in order to reach a plate with a differentpotential, such as the common plate(s) 4006. As noted, the shieldingplate 4009 may be positioned advantageously to cause the electric fieldlines 4004, 4005 to be directed downward and then out and around theedges or sides of the obscured feature detector 4001. For example, insome embodiments the shielding plate 4009 may be located on a layerdirectly above (e.g., away from a surface through which the obscuredfeature detector 4001 may be detecting an object) the sensor plates 4008and cover the entire area of the sensor plates 4008.

By configuring the electric field lines 4004, 4005 to curve around thesides of the obscured feature detector 4001, the electric field lines4004, 4005 may be able to penetrate further into a sensed object 4090and/or further into a surface to sense an obscured object than were theyconfined to the area directly in front of the sensor plates. Deeperpenetration of the electric field lines 4004, 4005 enables the sensorplates 4008 to yield more accurate and/or consistent readings,particularly as a thickness of the sensed object 4090 and/or a thicknessof a surface of detection changes.

The embodiments herein may be used for a variety of purposes other thandetecting obscured features. FIG. 40 provides an illustrative example ofusing an embodiment of an obscured feature detector 4001 for sensing anobject 4090. For example, in a manufacturing or production-lineenvironment that involves the handling or testing of biologicalproducts, a disclosed embodiment may be employed to detect whether ornot a product has changed its electro-chemical properties. If, tofurther the example, the product at hand is a type of produce such as afruit or vegetable, the product may change its dielectric properties(such as its relative static permeability) as it decomposes or variesits ripeness. Since capacitance is a function of the relative staticpermeability (otherwise known as the dielectric constant) of thematerial between two capacitive plates, the capacitance measured by theembodiment may vary when products of different ripeness pass through thesensing fields. In this example, an obscured feature detector accordingto one embodiment of the present disclosure may be used to sense whetheror not a product is within a desired specification of ripeness. Sincethe obscured feature detector may use a multitude of sensor plates, themeasurement may be able to provide more resolution of detail than whatwould be possible if only a single pair of capacitive plates were beingused.

Another application of the disclosed embodiments may involve theinvestigation of the electrical properties of various materials. In somesituations, it may be important to determine some electrical propertiesof a material without altering the position, shape, or structuralintegrity of the material. A disclosed embodiment on or near thematerial at hand may measure the capacitance and possibly compare themeasurement to that of a reference material. The capacitance measured,or the difference in capacitances when compared against a referencematerial, may yield a variety of details regarding the electricalproperties of the material at hand.

The disclosed embodiments may also be used to provide details about thecurvature or shape of a surface. If a disclosed embodiment is utilizedalong a curved or angled surface, for example, sensor plate readings mayyield different values depending on a distance of the sensor plate fromthe surface. From the variations in sensor values, the disclosedembodiments may be able to provide insight with regards to the gradientor angle of the surface.

The sensor values may also vary according to the texture of the materialwithin the sensing field. For example, if the material at hand isporous, grainy, rough, smooth, fibrous, or otherwise textured, thedisclosed embodiments may be employed to provide details about thattexture. In some applications, it may be possible to use the disclosedembodiments to make inferences regarding the density of a givenmaterial, or to determine other quality characteristics of a productthat dependent upon its dielectric constant.

Another application of the disclosed embodiments may involve determiningif a container is filled to the proper level, or if it has the rightquantity of items.

FIG. 41 is a view of a sensor plate cluster 4100 that includes sensorplates 4013, an active shield plate 4102, an active shield center 4101,and a common ring 4105. FIG. 41 shows eight sensor plates 4103. Thesensor plates 4103 are arranged radially around a center location. Inoperation the sensor plates 4103, the active shield plate 4102, and theactive shield center 4101 may all be driven simultaneously with a commonsignal. The sensor plates 4103, the active shield plate 4102, and theactive shield center 4101 may not be electrically coupled to each other,but because they are each driven with the same signal the electric fieldthat they create may be equivalent to the electric field that would becreated if they were each coupled to each other. Together they may formthe first end of a common electric field.

There is a common ring 4105 that may form the second end of the commonelectric field. In some embodiments the common ring 4105 is driven with0 volts. In other embodiments it may be driven with a differentunchanging voltage, or with an alternating voltage. Although there iscommon electric field that is created by the sensor plates 4103, theactive shield plate 4102, and active shield center 4101 all drivingtogether, nevertheless each element contributes to a particular portionof the common electric field. For example, the portion of the electricfield that is driven from the sensor plate 4103 on the lower-left sideof the sensor plate cluster 4100 will be located primarily in thelower-left side of the sensor plate cluster 4100. For example, the fieldlines from the lower-left sensor plate 4110 may originate at thatparticular sensor plate 4110. The field lines from the lower-left sensorplate 4110 will surrounded by field lines from the active shield center4101, and field lines from the active shield plate 4102, and field linesfrom neighboring sensor plates. It is as though the field lines from thelower left sensor plate 4110 are being guided by the field lines fromthe surrounding elements in the sensor plate cluster 4100. For example,the field lines from the neighboring sensor plates will bound thelower-left sensor plate 4110 field lines on either side. The field linesfrom the active shield plate 4102 will bound the field lines from thelower-left sensor plate 4110 on the top (where the top is the part offield that is furthest from the plane of the sensor plates). Likewisethe field lines from the active shield plate 4012 will bound the fieldlines from the lower-left sensor plate 4110 on the bottom. If therelative geometries and positions of surrounding elements change thefield lines from the lower-left sensor plate will likewise change.

By configuring surrounding electric fields, a product designer cancontrol what is being sensed because each sensor plate will primarilysense in the path of its respective electric fields. Using thistechnique it is possible to control where the electric fields will belocated. For example, to sense less of the material (e.g., the surface)that is close to the plane of a sensor plate 4103, a product designermay increase the active shield plate distance 4104 (e.g., a dimension ofa separation between a sensor plate 4103 and the common ring 4105). Forexample, a product designer may choose to reduce the size of the sensorplates 4103 by simultaneously increasing the active shield platedistance 4104. Implementing this design change will raise the lowerbound on the sensor plate field lines such that the sensed field linesare located along an arc that is further (e.g., deeper into the sensedsurface) from the plane of the sensor plate 4103. It may be advantageousto avoid sensing inconsistencies in the surface. For example, if thesurface was a wall made of sheetrock there could be inconsistenciescould be due to air bubbles in the sheetrock, variations in surfacetexture, inconsistencies in the paint, inconsistencies due to seamsbetween sheets of sheetrock, or other factors. In some embodiments itmay be preferable to sense less of the inconsistencies in the surface sothat sensor plate readings would be more representative of obscuredfeatures that may be further from the plane of the sensor plate 4103,which it may be desirable to read.

FIG. 42 is an alternate sensor plate cluster 4200 that includes sensorplates 4203, an active shield plate 4202, and an active shield center4201. The sensor plate cluster 4200 of FIG. 42 may be used in theobscured feature detector shown 4300 in FIG. 43. The embodimentsillustrated in FIGS. 42 and 43 may function very similarly to theconfiguration in FIG. 41, with a difference being the location of thecommon plate on the opposite side of the PCB. Positioning the commonplate on the opposite side of the PCB may cause the field lines toextend deeper into the surface and may drive the field lines furtheracross a broader spectrum of an obscured feature. As a result, obscuredfeature detectors that include the design of FIG. 42 and FIG. 43 maysense more deeply into a sensed surface, and may sense over a broaderarea compared to the configuration in FIG. 41.

FIG. 43 is a side view of an embodiment of an obscured feature detector4300 that may use the sensor plate cluster 4200 shown in FIG. 42. Theobscured feature detector 4300 is positioned on a surface 2. There is ahandle 4314 by which a user can grasp the device and a button 4324 thatthe user may actuate or otherwise manipulate to turn on the obscuredfeature detector 4300. A light pipe 4318 may guide the light from theindicators 4316 on a PCB 4330 to a location where the user may view thelight from the indicators 4316. The PCB 4330 may include be four layers.The top layer 4344 may include a majority of circuitry of the PCB 4330.A second layer 4343 of the PCB 4330 may include various routing ofsignals. The third layer may comprise an active shield layer 4202. Theactive shield layer 4202 may cover or otherwise encompass nearly theentire third layer of the PCB 4330, thereby shielding the sensor plates4203 from the sensing circuitry of the top layer 4344. The sensor plates4203 may be disposed on the fourth layer. There is also an active shieldcenter 4201 that is in the center of the PCB 4330 on the fourth layer.

In one embodiment, the sensor plates 4203, the active shield center4201, and the active shield layer 4202 are all driven with the samesignal. In other words, each is driven with signals that have the samevoltage at the same point in time. Because they are driven together,they create an electric field together. As a result the electric fieldthat is created is the same electric field that may be created if theactive shield layer 4202, and sensor plates 4203, and active shieldcenter 4201 were all electrically coupled to each other, because theyare each driven with the same signal. Together the active shield layer4202, and sensor plates 4203, and active shield center 4201 all form afirst end of an electric field. The electric fields 4304, 4305 may allhave a second end of the electric field at a hand guard common plate4306. In this embodiment, edge electric fields 4305 that are near theedge of the sensor plate cluster 4200 are driven by the active shieldlayer 4202. These edge electric fields 4305 may originate at the activeshield layer 4302 that is near the edge. In this embodiment theypenetrate the surface 2, then wrap around and terminate at the handguard common plate 4306. In some embodiments the hand guard common plate4306 is driven with 0 volts. In other embodiments, the hand guard commonplate 4306 may be driven with a different unchanging voltage, or with analternating voltage. These edge electric fields 4305 may not penetratedeeply enough to pass through the obscured feature 3. Because theseelectric fields only penetrate the surface 2 and may not penetratedeeply enough to reach the obscured features, the edge electric fieldsmay only vary depending upon the properties of the surface 2. Forexample if there are inconsistencies in the surface 2, the edge electricfield 4305 will experience a corresponding change. Advantageously, theedge electric field 4305 may not be sensed by the sensor plates 4305.

For many applications the sensor plaster cluster 4200 shown in FIG. 42may function better than the sensor plate cluster shown in FIG. 22. Thesensor plate cluster 4200 shown in FIG. 42 may avoid sensing some of thesurface inconsistencies so that the sensor plate readings are betterfocused on the obscured features that may be further from the plane ofthe sensor plates 4203. This will advantageously allow the obscuredfeature detector 4300 to sense more accurately and more deeply.

FIG. 44 is a sensor plate cluster 4413 of an obscured feature detector,according to one embodiment. The sensor plate cluster 4413 includesmultiple sensor plates 4404, 4405, 4406. The sensor plates 4404, 4405,4406 are configured to form the first end of an electric field. A commonplate 4401 is configured to form a second end of the electric field. Anactive shield plate 4410 is disposed between the sensor plates 4404,4405, 4406 and the common plate 4401 and is driven with a voltage. Inthis embodiment of FIG. 44, the end sensor plates 4404 have less surfacearea than the non-end sensor plates 4406. There is a common plate width4412, and an active shield plate width 4411, and a non-end sensor platewidth 4407, and an end sensor plate width 4408. There is also an activeshield region plate 4403. The active shield region plate 4403 may be ona different plane. In FIG. 44 the active shield region plate 4403 isrepresented by the white space on the printed circuit board because inthe illustrated embodiment it is on a different layer of the PCB.

In this illustrated embodiment of FIG. 44, the sensor plates 4404, 4405,4406 are driven with a signal. The active shield plate 4410 and activeshield region plate 4403 are driven with the same signal as the sensorplates 4404, 4405, 4406. Likewise when one sensor plate 4404, 4405, 4406is sensed the other sensor plates 4404, 4405, 4406 in the array aredriven with the same voltage signal.

The smaller sensor area of the end sensor plates 4404 may make the endsensor plates 4404 less responsive to changes in a surface 2, such thatthe responsiveness of the end sensor plates 4404 more closely matchesthe responsiveness of the non-end sensor plates 4405, 4406. Further, anelectric field formed between an end sensor plate 4404 and the commonplate 4401 will be smaller than were the surface area end sensor plate4404 identical (or closely similar) to the surface area of the non-endsensor plates 4405, 4406. In other words, the smaller surface area ofthe end sensor plate 4404 results in a smaller electric field that ismore similar in shape (including more similar in depth into the surfaceof detection) to the electric field between a non-end sensor plate 4405,4406 and the common plate 4401. An electric field between a smaller areaend sensor plate 4404 and the common plate 4401 does not diverge asdrastically as an end sensor plate having the same surface area as anon-end sensor plate. The electric fields between the end sensor plates4404 and the common plate 4401 are more similar to the electric fieldsbetween non-end sensor plates 4405, 4406 and the common plate 4401. Asnoted previously, the more similar shape of the electric fieldtranslates in more predictable readings of the sensor plates, andthereby more accurate detections of obscured features.

FIG. 45 is a side view of an obscured feature detector 4500 that may usethe sensor plate cluster 4413 that is shown in FIG. 44. The obscuredfeature detector 4500 includes a handle 14 that a user may grip to graspthe device, and a button 24 that can be actuated to turn on the obscuredfeature detector 4500. In FIG. 45, the obscured feature detector 4500 ispositioned on a surface 2.

A light pipe 8 may guide the light from the indicators 6 on the PCB to alocation where the user may view the light from the indicators 6. Theobscured feature detector 4500 may include a four-layer PCB 4510. Mostof the sensing circuitry, which is not shown, may be disposed on the toplayer 44 of the PCB 4510. The second layer 43 of the PCB 4510 mayinclude various routing of signals. A third layer of the PCB 4510includes an active shield layer 4513. On the fourth layer are disposedsensor plates 4406, a common plate 4401, and an active shield plate4410.

In one embodiment, the sensor plates 4406, the active shield plate 4410,and the active shield layer 4513 are all driven with the same voltagesignal. In other words, each is driven with signals that havesubstantially the same voltage at the same point in time. As they aredriven together, they create an electric field together. As a result theelectric field that is created may be the same electric field that wouldbe created if the active shield layer 4513, and sensor plates 4406, andactive shield plate 4410 were all electrically coupled to each other,because they are each driven with the same signal. Together the activeshield layer 4513, and sensor plates 4406, and active shield plate 4410all form a first end of an electric field. The electric fields 4501,4502, 4503, 4504, 4505 may all have a second end at the common plate4401.

In the embodiment shown in FIG. 45 there are five electric field lines4501, 4502, 4503, 4504, and 4505 that are illustrated. There are threesensed electric field lines 4501, 4502, and 4503. There are likewise twoun-sensed electric field lines 4504, 4505. In the embodiment shown inFIG. 45 it may be desirable to sense objects in the obscured featureregion 4508, and to avoid sensing the surface 2.

Although all of the electric field lines comprise a common electricfield only the portion of the field that is driven by the sensor plates4406 may be sensed. The electric fields 4504, 4505 that are driven bythe active shield plate 4410 may not penetrate deeply enough to passthrough the obscured feature 3. Because these electric fields 4504, 4505only penetrate the surface 2 and may not penetrate deeply enough toreach the obscured features, a reading of the un-sensed electric fields4504, 4505 may only vary depending upon the properties of the surface 2.For example if there are inconsistencies in the surface 2 the un-sensedelectric field 4504 and 4505 will experience a corresponding change.Advantageously the un-sensed electric fields 4504 and 4505 may not besensed by the sensor plates 4406.

A product designer can vary the relative sizes of the differentcomponents, namely the sensor plates 4406, the active shield plate 4410,and the common plate 4401, to target the sensing at the desired depth.For example, if the surface 2 is relatively thin it may be desirable tohave an active shield plate 4410 that is relatively narrow so that onlya very small portion of the field will not be sensed. Likewise, todetect obscured features that are further from the sensor plates 4406,or to sense through a thicker surface 2, it may be desirable to have anactive shield plate 4410 that is relatively wide so that the sensingfield is directed deeper. Likewise to sense through a surface 2 with alot of inconsistency it may be preferred to have a wider active shieldplate 4410 so that the sensed fields sense less of the surface 2.

It is understood that the sensed electric field lines 4501, 4502, 4503will need to pass through the surface 2 twice in order to detect anobscured feature 3. So the sensor plate 4406 readings will be vulnerableto inconsistencies in the surface 2 in the region where these fieldlines pass. Fortunately, however, by not sensing field lines that onlypass through the surface 2 the quality of the sensing may be improved.The result being that the sensor plates 4406 can better identify alocation of obscured features 3 because the readings may not be cloudedby inconsistencies in the surface 2. The result being that it ispossible to be selective about where what material is being sensed.

In order to be effective, the active shield plate 4410 may be positionedbetween the common plate 4401 at the sensor plates 4404, 4405, 4406 sothat the electric fields generated from the active shield plate 4410 mayin effect push the sensed field lines deeper into and through thesurface 2. The width of the active shield plate 4410 may vary byapplication. It may be recommended for many applications that theminimum dimension for the active shield plate width is about 18% of thetotal width of the sum of the width of the non-end sensor plate width4407, plus the active shield plate width 4411, plus common plate width4412. For many applications a suitable active shield plate width may bemuch larger. For example 30% may improve performance in manyapplications, and 40% may be an additional improvement. Likewise valuesfor the active shield plate width that are closer to 50% of the totalwidth of the sum of the width of the non-end sensor plate width 4407,plus the active shield plate width 4411, plus common plate width 4412may be ideal for many applications.

In terms of hard dimensions a 13 millimeter wide active shield platewidth may be a minimal dimension, with better performance at 20millimeters, 25 millimeters, or 30 millimeters wide. Those skilled inthe art can determine the dimensions suitable for a particularapplication.

In some embodiments the active shield, which may be on the active shieldplate 4410, is driven with a voltage signal that is the same as thevoltage signal on the sensor plates 4406. In some embodiments the activeshield is driven with an unchanging voltage, such as 0V. In someembodiments the active shield is driven with a voltage signal that is aratio of the sensor plate voltage signal, wherein the ratio may be morethan one, or less than one, such that the active shield voltage signalmay be larger than the sensor plate voltage signal or less than thesensor plate voltage signal. In some embodiments the active shield ispositioned between the common plate 4401 and the sensor plates 4406. Ifthe active shield voltage signal is greater than the sensor platevoltage signal it may have the effect of driving the sensor plateelectric fields deeper into the surface. Likewise if the active shieldvoltage signal is less than the sensor plate voltage signal it may havethe effect of driving the sensor plate electric fields less deeply intothe surface. In some embodiments the magnitude of the active shieldvoltage level can be changed by the user, or by the controller to senseat different depths. In some embodiments an image of the obscuredfeatures at different depths can be ascertained by performing multiplesensor plate reads with different active shield voltage signals. Suchreadings may also be performed by an array of sensor plates in a linear,or grid-like array to create an image of obscured features.

FIG. 46 is a side view of an obscured feature detector 4600, which issimilar to the obscured feature detector 4500 of FIG. 45. A differencebetween the obscured feature detector 4500 in FIG. 45 and the obscuredfeature detector 4600 of FIG. 46 is the position of the common plate4620 relative to the sensor plates 4606 and active shield plates 4610.In the obscured feature detector 4600 in FIG. 46 the active shield layer4613 is substantially between the sensor plates 4606 and the commonplate 4620. The obscured feature detector 4600 in FIG. 46 may beconfigured to cause the field lines (e.g., the electric fields 4601,4602, 4603, 4604, 4605) to penetrate more deeply into the surface, andmay enable obscured feature detectors that can sense more deeply, orthat have a smaller size. In the embodiment illustrated in FIG. 46 thefield lines travel more than 180 degrees along an arc between the commonplate 4620 and the sensor plates 4606. In some embodiments the commonplate 4620 and sensor plates 4606 are on opposite sides of the activeshield 4613. In some embodiments the common plate 4620 and sensor plates4606 are on opposite sides of the printed circuit board 4610.

The obscured feature detector 4600 includes a handle 14 that a user maygrip to grasp the device, and a button 24 that can be actuated to turnon the obscured feature detector 4500. In FIG. 46, the obscured featuredetector 4600 is positioned on a surface 2.

A light pipe 8 may guide the light from the indicators 6 on a PCB 4610to a location where the user may view the light from the indicators 6.The obscured feature detector 4600 may include a four-layer PCB 4610.Most of the sensing circuitry, which is not shown, may be disposed onthe top layer 44 of the PCB 4610. The second layer 43 of the PCB 4610may include various routing of signals. A third layer of the PCB 4610may include an active shield layer 4613. On the fourth layer aredisposed sensor plates 4606, and an active shield plate 4610.

In one embodiment, the sensor plates 4606, the active shield plate 4610,and the active shield layer 4613 are all driven with the same voltagesignal. In other words, each is driven with signals that havesubstantially the same voltage at the same point in time. As they aredriven together, they create an electric field together. As a result theelectric field that is created may be the same electric field that wouldbe created if the active shield layer 4613, and sensor plates 4606, andactive shield plate 4610 were all electrically coupled to each other,because they are each driven with the same signal. Together the activeshield layer 4613, and sensor plates 4606, and active shield plate 4410all form a first end of an electric field 4601, 4602, 4603, 4604, 4605.Each electric field 4601, 4602, 4603, 4604, 4605 may all have a secondend at the common plate 4620.

In the embodiment shown in FIG. 46, five electric field lines 4601,4602, 4603, 4604, 4605 are illustrated. There are three sensed electricfield lines 4601, 4602, 4603. There are likewise two un-sensed electricfield lines 4604, 4605. In the embodiment shown in FIG. 46 it may bedesirable to sense objects in the obscured feature region 4608, and toavoid sensing the surface 2.

Although all of the electric field lines 4601, 4602, 4603, 4604, 4605comprise a common electric field only the portion of the field that isdriven by the sensor plates 4606 may be sensed. The electric fields4604, 4605 that are driven by the active shield plate 4610 may notpenetrate deeply enough to pass through an obscured feature 3. Becausethese electric fields 4604, 4605 only penetrate the surface 2 and maynot penetrate deeply enough to reach the obscured features, a reading ofthe un-sensed electric fields 4604, 4605 may only vary depending uponthe properties of the surface 2. For example if there areinconsistencies in the surface 2 the un-sensed electric field 4604 and4605 will experience a corresponding change. Advantageously theun-sensed electric fields 4604 and 4605 may not be sensed by the sensorplates 4606.

A product designer can vary the relative sizes of the differentcomponents, namely the sensor plates 4606, the active shield plate 4610,and the common plate 4620, to target the sensing at the desired depth.For example, if the surface 2 is relatively thin it may be desirable tohave an active shield plate 4610 that is relatively narrow so that onlya very small portion of the field will not be sensed. Likewise, todetect obscured features that are further from the sensor plates 4606,or to sense through a thicker surface 2, it may be desirable to have anactive shield plate 4610 that is relatively wide so that the sensingfield is directed deeper. Likewise to sense through a surface 2 with alot of inconsistency it may be preferred to have a wider active shieldplate 4610 so that the sensed fields sense less of the surface 2. Insome embodiments the designer may select the area to be sensed bychanging the size and position of the sensor plates 4606, active shieldplate 4610, and common plate 4620.

EXAMPLES

The following are some example embodiments within the scope of thedisclosure. In order to avoid complexity in providing the disclosure,not all of the examples listed below are separately and explicitlydisclosed as having been contemplated herein as combinable with all ofthe others of the examples listed below and other embodiments disclosedhereinabove. Unless one of ordinary skill in the art would understandthat these examples listed below, and the above disclosed embodiments,are not combinable, it is contemplated within the scope of thedisclosure that such examples and embodiments are combinable.

Example 1

An obscured feature detector comprising: three or more sensor platesarranged linearly to form a sensor array, each of the three or moresensor plates configured to form a first end of a corresponding electricfield and to take a sensor reading of the corresponding electric field,wherein the corresponding electric field varies based on a proximity ofthe sensor plate to one or more surrounding objects and on a materialproperty of each of the one or more surrounding objects, wherein an endsensor plate at an end of the sensor array has a smaller area than anon-end sensor plate that is not at the end of the sensor array; acommon plate to form a second end of the corresponding electric field ofone or more sensor plates of the three or more sensor plates; a sensingcircuit coupled to the three or more sensor plates, the sensing circuitbeing configured to measure the sensor readings on the three or moresensor plates; and an indicator to be toggled between a deactivatedstate and an activated state to indicate a location of a region ofrelative high sensor reading.

Example 2

The obscured feature detector of Example 1, wherein each of the sensorplates form an electric field with a single common plate of the one ormore common plates.

Example 3

The obscured feature detector of Example 1, wherein the three or moresensor plates are each driven with the same signal simultaneously.

Example 4

The obscured feature detector of Example 1, wherein the end sensor plateis configured such that the corresponding electric field formed by theend sensor plate is geometrically similar to the corresponding electricfield formed by a middle sensor plate.

Example 5

The obscured feature detector of Example 1, wherein the sensor array andthe common plate lie in a common plane that is to be parallel to asurface that obscures a detected feature at a time of detection.

Example 6

The obscured feature detector of Example 5, wherein the three or moresensor plates are each driven with the same signal simultaneously.

Example 7

The obscured feature detector of Example 5, wherein the three or moresensor plates are each driven with the same signal simultaneously andwherein the sensing circuit measures the sensor reading of one of thethree or more sensor plates.

Example 8

The obscured feature detector of Example 1, further comprising an activeshield, wherein the three sensor plates and the active shield are eachdriven with the same signal simultaneously.

Example 9

The obscured feature detector of Example 1, wherein the three sensorplates and an active shield are each driven with the same signalsimultaneously and wherein the sensing circuit measures the sensorreading of only one of the sensor plates.

Example 10

The obscured feature detector of Example 1, wherein the common platecomprises a set of multiple individual plates, each individual plateforming a second end of the corresponding electric field of a sensorplate of the three or more sensor plates.

Example 11

The obscured feature detector of Example 10, wherein each of themultiple individual plates is independently activated.

Example 12

The obscured feature detector of Example 1, wherein a width dimension ofthe end plate is less than a width dimension of the non-end sensorplate.

Example 13

The obscured feature detector of Example 1, wherein a width dimension ofa first end of the end plate is less than a width dimension of a secondend of the end plate.

Example 14

The obscured feature detector of Example 1, wherein all non-end sensorplates of the three or more sensor plates have the same dimensions.

Example 15

The obscured feature detector of Example 1, wherein a voltage signal isdriven on the common plate, wherein a reading is taken on a sensor plateof the three or more sensor plates, and wherein the reading is relativeto the capacitance between the common plate and the sensor plate.

Example 16

An obscured feature detector comprising: three or more sensor platesarranged linearly to form a sensor array, each of the sensor plateconfigured to form a first end of a corresponding electric field and totake a sensor reading of the corresponding electric field, wherein thecorresponding electric field varies based on a proximity of the sensorplate to one or more surrounding objects and on a material property ofeach of the one or more surrounding objects, wherein each end sensorplate at an end of the sensor array has dimensions different fromdimensions of a non-end sensor plate that is not at the end of thesensor array, the dimensions of the end sensor plates configured suchthat the corresponding electric field formed by each of the end sensorplates is geometrically similar to the corresponding electric fieldformed by a middle sensor plate; a common plate to form a second end ofthe corresponding electric field of one or more sensor plates on thethree or more sensor plates; a sensing circuit coupled to the three ormore sensor plates, the sensing circuit being configured to measure thesensor readings of the three or more sensor plates; and an indicator tobe toggled between a deactivated state and an activated state toindicate a location of a region of relative high sensor reading.

Example 17

The obscured feature detector of Example 16, wherein the three or moresensor plates are each driven with the same signal simultaneously.

Example 18

The obscured feature detector of Example 16, wherein the sensor arrayand the common plate both lie in a plane that is to be parallel to asurface that obscures a detected feature at a time of detection.

Example 19

The obscured feature detector of Example 16, further comprising anactive shield, wherein the three sensor plates and the active shield areeach driven with the same signal simultaneously.

Example 20

The obscured feature detector of Example 16, wherein a width dimensionof the end plate is less than a width dimension of the non-end sensorplate.

Example 21

The obscured feature detector of Example 16, wherein a width dimensionof a first end of the end plate is less than a width dimension of asecond end of the end plate.

Example 22

The obscured feature detector of Example 16, wherein a voltage signal isdriven on the common plate, wherein a reading is taken on a sensor plateof the three or more sensor plates, and wherein the reading is relativeto the capacitance between the common plate and the sensor plate.

Example 23

A method of detecting an obscured feature behind a surface, comprising:taking a sensor reading of three or more sensor plates of an obscuredfeature detector that is disposed on a surface, the three or more sensorplates arranged linearly in a sensor array, wherein an end sensor platehas a smaller area than a non-end sensor plate, and wherein the sensorreading is taken of a region of a sensing field formed between the threeor more sensor plates and a common plate of the obscured featuredetector; measuring, via a sensing circuit, the sensor readings of thethree or more sensor plates; comparing measurements of sensor readingsin different regions of the sensing field; and toggling an indicatorfrom a deactivated state to an activated state to indicate a location ofa region of the sensing field having a relatively high sensor reading.

Example 24

The method of Example 23, further comprising driving an active shield ofthe obscured feature detector with the same signal as the three or moresensor plates to form the sensing field.

Example 25

The method of Example 23, wherein the measured sensor reading is acapacitive reading.

Example 26

The method of Example 23, wherein the measured sensor reading is anelectromagnetic reading.

Example 26

The method of Example 23, wherein a width dimension of the end plate isless than a width dimension of the non-end sensor plate.

Example 27

The method of Example 23, wherein a width dimension of a first end ofthe end plate is less than a width dimension of a second end of the endplate.

Example 28

An obscured feature detector comprising: three or more sensor platesarranged along a length to form a sensor array, each of the three ormore sensor plates configured to form a first end of a correspondingelectric field and to take a sensor reading of the correspondingelectric field, wherein the corresponding electric field varies based ona proximity of the sensor plate to one or more surrounding objects andon a material property of each of the one or more surrounding objects, acommon plate to form a second end of the corresponding electric field ofone or more sensor plates of the three or more sensor plates; an activeshield plate that is driven with a voltage signal, wherein the activeshield plate is positioned between the sensor plates and the commonplate, and wherein the active shield has a width dimension that ismeasured perpendicular to the length of the sensor array, wherein theactive shield width is more than 18% of a combined width of the commonplate, the active shield zone, and a sensor plate of the three or moresensor plates; a sensing circuit coupled to the three or more sensorplates, the sensing circuit being configured to measure the sensorreadings on the three or more sensor plates; and an indicator to betoggled between a deactivated state and an activated state to indicate alocation of a region of relative high sensor reading.

Example 29

The obscured feature detector of Example 28, wherein a plurality ofsensor plates of the three or more sensor plates are driven with thesame signal simultaneously.

Example 30

The obscured feature detector of Example 28, wherein a plurality ofsensor plates of the three or more sensor plates and the active shieldplate are each driven with the same signal simultaneously.

Example 31

The obscured feature detector of Example 28, wherein increasing thevoltage level of the signal on the active shield causes the field linesfrom a sensor plate of the three or more sensor plates to take a paththat is further from the plane of the sensor plate.

Example 32

The obscured feature detector of Example 28, wherein the active shieldplate is driven with a static voltage level.

Example 33

The obscured feature detector of Example 28, wherein the active shieldplate is driven with a non-static voltage level.

Example 34

The obscured feature detector of Example 28, wherein the voltage signalon the active shield plate matches a voltage signal that is on a sensorplate of the three or more sensor plates.

Example 35

The obscured feature detector of Example 28, wherein the voltage signalon the active shield plate is a ratio of a voltage signal that is on asensor plate of the three or more sensor plates.

Example 36

The obscured feature detector of Example 28, wherein a first sensorplate of the three or more sensor plates has more surface area than asecond sensor plate of the three or more sensor plates.

Example 37

The obscured feature detector of Example 28, wherein the active shieldplate, the common plate, and the three or more sensor plates aresubstantially in the same plane.

Example 38

The obscured feature detector of Example 28, wherein a voltage signal isdriven on the common plate, and wherein a reading is taken on a sensorplate of the three or more sensor plates and the reading is relative toa capacitance between the common plate and the sensor plate.

Example 39

An obscured feature detector comprising: three or more sensor platesarranged along a length to form a sensor array, each of the three ormore sensor plates configured to form a first end of a correspondingelectric field and to take a sensor reading of the correspondingelectric field, wherein the corresponding electric field varies based ona proximity of the sensor plate to one or more surrounding objects andon a material property of each of the one or more surrounding objects, acommon plate to form a second end of the corresponding electric field ofone or more sensor plates of the three or more sensor plates; an activeshield plate that is driven with a voltage, wherein the active shieldplate is configured to influence the electric fields between the threeor more sensor plates and the common plate, and wherein the activeshield has a width that is perpendicular to the length of the sensorarray, wherein the active shield plate width is more than 18% of thecombined width of the common plate, the active shield zone, and a sensorplate; a sensing circuit coupled to the three or more sensor plates, thesensing circuit being configured to measure the sensor readings on thethree or more sensor plates; and an indicator to be toggled between adeactivated state and an activated state to indicate a location of aregion of relative high sensor reading.

Example 40

The obscured feature detector of Example 39, wherein a plurality ofsensor plates of the three or more sensor plates are driven with thesame signal simultaneously.

Example 41

The obscured feature detector of Example 39, wherein a plurality ofsensor plates of the three or more sensor plates and the active shieldplate are each driven with the same signal simultaneously.

Example 42

The obscured feature detector of Example 39, wherein increasing thevoltage level of the signal on the active shield causes the field linesfrom a sensor plate of the three or more sensor plates to take a paththat is further from the plane of the sensor plate.

Example 43

The obscured feature detector of Example 39, wherein the active shieldplate is driven with a static voltage level.

Example 44

The obscured feature detector of Example 39, wherein the active shieldplate is driven with a non-static voltage level.

Example 45

The obscured feature detector of Example 39, wherein the voltage signalon the active shield plate matches a voltage signal that is on a sensorplate of the three or more sensor plates.

Example 46

The obscured feature detector of Example 39, wherein the voltage signalon the active shield plate is a ratio of a voltage signal that is on asensor plate of the three or more sensor plates.

Example 47

The obscured feature detector of Example 39, wherein a first sensorplate of the three or more sensor plates has more surface area than asecond sensor plate of the three or more sensor plates.

Example 48

The obscured feature detector of Example 39, wherein the active shieldplate, the common plate, and the three or more sensor plates aresubstantially in the same plane.

Example 49

The obscured feature detector of Example 39, wherein a voltage signal isdriven on the common plate, and wherein a reading is taken on a sensorplate of the three or more sensor plates and the reading is relative toa capacitance between the common plate and the sensor plate.

Example 50

An obscured feature detector comprising: three or more sensor platesarranged along a length to form a sensor array, each of the three ormore sensor plates configured to form a first end of a correspondingelectric field and to take a sensor reading of the correspondingelectric field, wherein the corresponding electric field varies based ona proximity of the sensor plate to one or more surrounding objects andon a material property of each of the one or more surrounding objects; acommon plate to form a second end of the corresponding electric field ofone or more sensor plates of the three or more sensor plates; an activeshield plate that is driven with a voltage, wherein the active shield isconfigured to influence the electric fields between the three or moresensor plates and the common plate, and wherein the active shield platehas a width that is perpendicular to the length of the sensor array,wherein the active shield width is more than 13 millimeters wide; asensing circuit coupled to the three or more sensor plates, the sensingcircuit being configured to measure the sensor readings of the three ormore sensor plates; and an indicator to be toggled between a deactivatedstate and an activated state to indicate a location of a region ofrelative high sensor reading.

Example 51

The obscured feature detector of Example 50, wherein a plurality ofsensor plates of the three or more sensor plates are driven with thesame signal simultaneously.

Example 52

The obscured feature detector of Example 50, wherein a plurality ofsensor plates of the three or more sensor plates and the active shieldplate are each driven with the same signal simultaneously.

Example 53

The obscured feature detector of Example 50, wherein increasing thevoltage level of the signal on the active shield causes the field linesfrom a sensor plate of the three or more sensor plates to take a paththat is further from the plane of the sensor plate.

Example 54

The obscured feature detector of Example 50, wherein the active shieldplate is driven with a static voltage level.

Example 55

The obscured feature detector of Example 50, wherein the active shieldplate is driven with a non-static voltage level.

Example 56

The obscured feature detector of Example 50, wherein the voltage signalon the active shield plate matches a voltage signal that is on a sensorplate of the three or more sensor plates.

Example 57

The obscured feature detector of Example 50, wherein the voltage signalon the active shield plate is a ratio of a voltage signal that is on asensor plate of the three or more sensor plates.

Example 58

The obscured feature detector of Example 50, wherein a first sensorplate of the three or more sensor plates has more surface area than asecond sensor plate of the three or more sensor plates.

Example 59

The obscured feature detector of Example 50, wherein the active shieldplate, the common plate, and the three or more sensor plates aresubstantially in the same plane.

Example 60

The obscured feature detector of Example 50, wherein a voltage signal isdriven on the common plate, and wherein a reading is taken on a sensorplate of the three or more sensor plates and the reading is relative toa capacitance between the common plate and the sensor plate.

Example 61

An obscured feature detector comprising: a group of three or more sensorplates arranged radially around a center point, each sensor plate of thethree or more sensor plates to form a first end of a correspondingelectric field and to take a sensor reading of the correspondingelectric field that varies based on a proximity of the sensor plate toone or more surrounding objects and on a material property of each ofthe one or more surrounding objects; a common plate to form a second endof the corresponding electric field of one or more sensor plates of thethree or more sensor plates; one or more active shield plates drivenwith a voltage and positioned outside of a perimeter of the group ofthree or more sensor plates; and a sensing circuit coupled to the threeor more sensor plates, the sensing circuit being configured to measurethe sensor readings of the three or more sensor plates.

Example 62

The obscured feature detector of Example 61, wherein the common plate isa ring disposed around the one or more active shield plates.

Example 63

The obscured feature detector of Example 61, wherein multiple sensorplates of the three or more sensor plates are driven with the samesignal simultaneously.

Example 64

The obscured feature detector of Example 61, wherein multiple sensorplates of the three or more sensor plates and the one or more activeshield plates are each driven with the same signal simultaneously.

Example 65

The obscured feature detector of Example 61, wherein increasing thevoltage on the one or more active shield plates causes the field linesfrom a sensor plate of the three or more sensor plates to take a path tothe common plate that is further from the plane of the three or moresensor plates.

Example 66

The obscured feature detector of Example 61, wherein the one or moreactive shield plates are driven with a static voltage level.

Example 67

The obscured feature detector of Example 61, wherein the one or moreactive shield plates are driven with a non-static voltage level.

Example 68

The obscured feature detector of Example 61, wherein the voltage signalon the one or more active shield plate matches a voltage signal that ison a sensor plate of the three or more sensor plates.

Example 69

The obscured feature detector of Example 61, wherein the voltage signalon the one or more active shield plates is a ratio of the voltage signalthat is on a sensor plate of the three or more sensor plates.

Example 70

The obscured feature detector of Example 61, wherein the active shieldplate, the common plate, and the three or more sensor plates aresubstantially in the same plane.

Example 71

The obscured feature detector of Example 61, wherein a voltage signal isdriven on the common plate, and wherein a reading is taken on a sensorplate of the three or more plates and the reading is relative to acapacitance between the common plate and the sensor plate.

Example 72

An obscured feature detector comprising: a group of two or more sensorplates arranged radially around a center point, each sensor plate of thetwo or more sensor plates to form a first end of a correspondingelectric field and to take a sensor reading of the correspondingelectric field that varies based on a proximity of the sensor plate toone or more surrounding objects and on a material property of each ofthe one or more surrounding objects; a common plate to form a second endof the corresponding electric field of one or more sensor plates; one ormore active shield plates to be driven with a voltage and positionedoutside of the perimeter of the group of two or more sensor plates; anda sensing circuit coupled to the two or more sensor plates, the sensingcircuit being configured to measure the sensor readings of the two ormore sensor plates.

Example 73

The obscured feature detector of Example 72, wherein an active shieldplate of the one or more active shield plates is positioned between thecommon plate and a sensor plate of the two or more sensor plates.

Example 74

The obscured feature detector of Example 73, wherein the common plate isapproximately perpendicular to the active shield plate.

Example 75

The obscured feature detector of Example 72, wherein the common plate isa ring disposed around the one or more active shield plates.

Example 76

The obscured feature detector of Example 72, wherein multiple sensorplates of the two or more sensor plates are driven with the same signalsimultaneously.

Example 77

The obscured feature detector of Example 72, wherein multiple sensorplates of the two or more sensor plates and the one or more activeshield plates are each driven with the same signal simultaneously.

Example 78

The obscured feature detector of Example 72, wherein increasing thevoltage on the active shield plate causes the field lines from a sensorplate of the two or more sensor plates to take a path to the commonplate that is further from the plane of the two or more sensor plates.

Example 79

The obscured feature detector of Example 72, wherein the active shieldplate is driven with a static voltage level.

Example 80

The obscured feature detector of Example 72, wherein the active shieldplate is driven with a non-static voltage level.

Example 81

The obscured feature detector of Example 72, wherein the voltage signalon the active shield plate matches a voltage signal that is on a sensorplate of the two or more sensor plates.

Example 82

The obscured feature detector of Example 72, wherein the voltage signalon the active shield plate is a ratio of the voltage signal that is on asensor plate of the two or more sensor plates.

Example 83

The obscured feature detector of Example 72, wherein the active shieldplate, the common plate, and the two or more sensor plates aresubstantially in the same plane.

Example 84

The obscured feature detector of Example 72, wherein a voltage signal isdriven on the common plate, and wherein a reading is taken on a sensorplate of the two or more plates and the reading is relative to acapacitance between the common plate and the sensor plate.

Example 85

An obscured feature detector comprising: a common plate positioned at acenter point of a bottom of the obscured feature detector; one or moreactive shield plates driven with a voltage and arranged radially aroundthe common plate; three or more sensor plates arranged radially aroundthe one or more active shield plates, each sensor plate to form acorresponding electric field with the common plate, each sensor plate totake a sensor reading of the corresponding electric field that variesbased on a proximity of the sensor plate to one or more surroundingobjects and on a material property of each of the one or moresurrounding objects; and a sensing circuit coupled to the three or moresensor plates, the sensing circuit being configured to measure thesensor readings of the three or more sensor plates.

Example 86

The obscured feature detector of Example 85, wherein multiple sensorplates of the three or more sensor plates are driven with the samesignal simultaneously.

Example 87

The obscured feature detector of Example 85, wherein multiple sensorplates of the three or more sensor plates and the one or more activeshield plates are each driven with the same signal simultaneously.

Example 88

The obscured feature detector of Example 85, wherein increasing thevoltage on the one or more active shield plates causes the field linesfrom a sensor plate of the three or more sensor plates to take a path tothe common plate that is further from the plane of the three or moresensor plates.

Example 89

The obscured feature detector of Example 85, wherein the one or moreactive shield plates are driven with a static voltage level.

Example 90

The obscured feature detector of Example 85, wherein the one or moreactive shield plates are driven with a non-static voltage level.

Example 91

The obscured feature detector of Example 85, wherein the voltage signalon the one or more active shield plates matches a voltage signal that ison a sensor plate of the three or more sensor plates.

Example 92

The obscured feature detector of Example 85, wherein the voltage signalon the one or more active shield plates is a ratio of the voltage signalthat is on a sensor plate of the three or more sensor plates.

Example 93

The obscured feature detector of Example 85, wherein the one or moreactive shield plates, the common plate, and the three or more sensorplates are substantially in the same plane.

Example 94

The obscured feature detector of Example 85, wherein a voltage signal isdriven on the common plate, and wherein a reading is taken on a sensorplate of the three or more plates and the reading is relative to acapacitance between the common plate and the sensor plate.

It will be obvious to those having skill in the art that many changesmay be made to the details of the above-described embodiments withoutdeparting from the underlying principles of the invention. The scope ofthe present invention should, therefore, be determined only by thefollowing claims.

The invention claimed is:
 1. An obscured feature detector comprising:three or more sensor plates arranged linearly to form a sensor array,each of the three or more sensor plates configured to form a first endof a corresponding electric field and to take a sensor reading of thecorresponding electric field, wherein the corresponding electric fieldvaries based on a proximity of the sensor plate to one or moresurrounding objects and on a material property of each of the one ormore surrounding objects, wherein an end sensor plate at an end of thesensor array has a smaller area than a non-end sensor plate that is notat the end of the sensor array; a common plate to form a second end ofthe corresponding electric field of one or more sensor plates of thethree or more sensor plates; a sensing circuit coupled to the three ormore sensor plates, the sensing circuit being configured to measure thesensor readings on the three or more sensor plates; and an indicator tobe toggled between a deactivated state and an activated state toindicate a location of a region of relative high sensor reading.
 2. Theobscured feature detector of claim 1, wherein each of the sensor platesform an electric field with a single common plate of the one or morecommon plates.
 3. The obscured feature detector of claim 1, wherein thethree or more sensor plates are each driven with the same signalsimultaneously.
 4. The obscured feature detector of claim 1, wherein theend sensor plate is configured such that the corresponding electricfield formed by the end sensor plate is geometrically similar to thecorresponding electric field formed by a middle sensor plate.
 5. Theobscured feature detector of claim 1, wherein the sensor array and thecommon plate lie in a common plane that is to be parallel to a surfacethat obscures a detected feature at a time of detection.
 6. The obscuredfeature detector of claim 5, wherein the three or more sensor plates areeach driven with the same signal simultaneously.
 7. The obscured featuredetector of claim 5, wherein the three or more sensor plates are eachdriven with the same signal simultaneously and wherein the sensingcircuit measures the sensor reading of one of the three or more sensorplates.
 8. The obscured feature detector of claim 1, further comprisingan active shield, wherein the three sensor plates and the active shieldare each driven with the same signal simultaneously.
 9. The obscuredfeature detector of claim 1, wherein the three sensor plates and anactive shield are each driven with the same signal simultaneously andwherein the sensing circuit measures the sensor reading of only one ofthe sensor plates.
 10. The obscured feature detector of claim 1, whereinthe common plate comprises a set of multiple individual plates, eachindividual plate forming a second end of the corresponding electricfield of a sensor plate of the three or more sensor plates.
 11. Theobscured feature detector of claim 10, wherein each of the multipleindividual plates is independently activated.
 12. The obscured featuredetector of claim 1, wherein a width dimension of the end plate is lessthan a width dimension of the non-end sensor plate.
 13. The obscuredfeature detector of claim 1, wherein a width dimension of a first end ofthe end plate is less than a width dimension of a second end of the endplate.
 14. The obscured feature detector of claim 1, wherein all non-endsensor plates of the three or more sensor plates have the samedimensions.
 15. The obscured feature detector of claim 1, wherein avoltage signal is driven on the common plate, wherein a reading is takenon a sensor plate of the three or more sensor plates, and wherein thereading is relative to the capacitance between the common plate and thesensor plate.
 16. An obscured feature detector comprising: three or moresensor plates arranged linearly to form a sensor array, each of thesensor plate configured to form a first end of a corresponding electricfield and to take a sensor reading of the corresponding electric field,wherein the corresponding electric field varies based on a proximity ofthe sensor plate to one or more surrounding objects and on a materialproperty of each of the one or more surrounding objects, wherein eachend sensor plate at an end of the sensor array has dimensions differentfrom dimensions of a non-end sensor plate that is not at the end of thesensor array, the dimensions of the end sensor plates configured suchthat the corresponding electric field formed by each of the end sensorplates is geometrically similar to the corresponding electric fieldformed by a middle sensor plate; a common plate to form a second end ofthe corresponding electric field of one or more sensor plates on thethree or more sensor plates; a sensing circuit coupled to the three ormore sensor plates, the sensing circuit being configured to measure thesensor readings of the three or more sensor plates; and an indicator tobe toggled between a deactivated state and an activated state toindicate a location of a region of relative high sensor reading.
 17. Theobscured feature detector of claim 16, wherein the three or more sensorplates are each driven with the same signal simultaneously.
 18. Theobscured feature detector of claim 16, wherein the sensor array and thecommon plate both lie in a plane that is to be parallel to a surfacethat obscures a detected feature at a time of detection.
 19. Theobscured feature detector of claim 16, further comprising an activeshield, wherein the three sensor plates and the active shield are eachdriven with the same signal simultaneously.
 20. The obscured featuredetector of claim 16, wherein a width dimension of the end plate is lessthan a width dimension of the non-end sensor plate.
 21. The obscuredfeature detector of claim 16, wherein a width dimension of a first endof the end plate is less than a width dimension of a second end of theend plate.
 22. The obscured feature detector of claim 16, wherein avoltage signal is driven on the common plate, wherein a reading is takenon a sensor plate of the three or more sensor plates, and wherein thereading is relative to the capacitance between the common plate and thesensor plate.
 23. A method of detecting an obscured feature behind asurface, comprising: taking a sensor reading of three or more sensorplates of an obscured feature detector that is disposed on a surface,the three or more sensor plates arranged linearly in a sensor array,wherein an end sensor plate has a smaller area than a non-end sensorplate, and wherein the sensor reading is taken of a region of a sensingfield formed between the three or more sensor plates and a common plateof the obscured feature detector; measuring, via a sensing circuit, thesensor readings of the three or more sensor plates; comparingmeasurements of sensor readings in different regions of the sensingfield; and toggling an indicator from a deactivated state to anactivated state to indicate a location of a region of the sensing fieldhaving a relatively high sensor reading.
 24. The method of claim 23,further comprising driving an active shield of the obscured featuredetector with the same signal as the three or more sensor plates to formthe sensing field.
 25. The method of claim 23, wherein the measuredsensor reading is a capacitive reading.
 26. The method of claim 23,wherein a width dimension of the end plate is less than a widthdimension of the non-end sensor plate.
 27. The method of claim 23,wherein a width dimension of a first end of the end plate is less than awidth dimension of a second end of the end plate.
 28. The method ofclaim 23, wherein the measured sensor reading is an electromagneticreading.